Programming in C++

MECH-215 TA
C++ Programming
Session #2
Jan 23 2013
Course Lecturer: Ted Obuchowicz
Tutor: Pooya Merat
Concordia University
Disclaimer: The contents provided in this file are intended only as a reference for TA class and might be incomplete or
incorrect. Any reliance upon detailed information presented in this file shall be at reader’s risk.

P. Merat Jan 23 2013

MECH-215 TA
Topics:






Data types
Identifiers
Variable Declaration
Basic User Interface
Practice


Data Types
Integer Numbers:
Syntax

Type

Range

char var1;
short var2;
short int var3;
long var4;
long int var5;
int var6;

Integer

-128 to 127

Integer

-32768 to 32767

Integer

-2147483648
2147483647

to

Any of above could be “unsigned” >> Whole number (from 0 - XX)
Example:
unsigned char var1;

Real Numbers:
Syntax

Type

Range

float Var1;
double Var2;

Real
Real

1e-38 to 3e38
2e-308 to 2e308


Identifiers
Identifiers are any programmer defined names such as:
Variable Names and Function Names
Rules
1. Cannot contain a white space:
int Variable One; // Wrong!

2.
Cannot start with a number (1…9) or contain any special
characters:
int 5_var; // Wrong!
int va$r; // Wrong!

3. Cannot be the exact C++ directives:
int while; // Wrong!


Identifiers (Example)
Which of these identifiers (variable names) are correct?

1) double a;
2) float My var;
3) double var1;

4) int > a;

6) short ?Ask;

5) char dWgGD_c123Y_5;
6) double float;

7) int aa+a;
8) long K.1;

A variable name should be a combination of only letters, digits and
underscore.
Note: C++ is case sensitive.
int Variable;

is different from
int vAriable;


Variable Declaration
You can declare variables of the same type like:
int alpha, beta, theta;

or:
int alpha,
beta,
theta;

or like this:
int alpha;
int beta;
int theta;


Basic User-Interface - cout
cout function:
// Print on the screen.
cout << "Life is short!";

is the same as:
cout << "Life " << "is " << "short!";

or you can write:
cout << "Life ";
cout << "is ";
cout << "short!";


Basic User-Interface - cout (Example)
cout function:
Print the value of a variable:
int myID = 1320006;
cout << "Your ID is: " << myID << endl;
// Output: Your ID is: 1320006

Next line:
cout << "n" ; // Go to the next line
cout << endl ; // Go to the next line


Basic User-Interface - cin
cin function:
int Integer_1;
cout << "Please enter an integer number: ";
// Get a number from the user
cin >> Integer_1;
// Confirm the number
cout << "You just entered number: " << Integer_1 << endl;


Practice
Find the errors in this code:
#include {iostream}
Using Namespace std;
int main[]
{
// Declare the first variable
int first var =
5;
// Declare the second variable
Int 2nd_Var;
// Print the sum of the two integers on the screen.
cout << "Sum is: first var + 2nd_VAR" << "n";
/* Note that "n" is the same as: endl */
Return0 ;
}


Practice (Answer)
Corrected code:
#include {iostream} // Must be : <iostream>
Using Namespace std; // Must be : using namespace std
int main[] // Must be : ()
{
//Declare 1st var
int first var =
5; // Could be
// Declare the second variable
Int 2nd_Var; // Could be : int Var2
// Print the
cout << "Sum
// Corrected
cout << "Sum
/* Note that

No change will occur with
this extra space here, but
It will not look good!
: first_var
= 15;

sum of the two integers on the screen.
is: first var + 2nd_VAR" << "n";
one is:
is: " << first_var + Var2 << "n";
"n" is the same as: endl*/

Return0 ; // Should be : return 0;
}


Common Types of Errors
1)

Syntax Errors

Compiler gives you an error and the output file is not created.
int 2nd_Var; // Bad variable name
integer Var2; // Wrong directive
int Var2 // Missing semicolon

2)

Semantic Errors

Compiler does not care (compiles with no errors), but you still do not
get your desired result.
// Print the sum of the two integers on the screen.
cout << "Sum is equal to : var1 + var2" << "n";
// but here it only prints var1 + var2 and not its value.

Could also be using the wrong variable type, the wrong operation,
etc.

Practice #1: Age Calculation
Write a program to ask the user’s year of birth and current year and
print out the user’s age and the expected death year (100 years after
birth).


Practice #2: Cannon Range
Write a code to get the angle (degrees) and velocity (m/s2) of cannon
and find its range (m). [ g = 9.81 ]

V
α

R

Here is the formula:
R = V2 sin(2α) / g


MECH-215 TA
C++ Programming
Session #3
Jan 30 2013
Tutor: Pooya Merat


MECH-215 TA
Topics:
 Priority of Math Operators
 Variable Type Change
 Relational and Boolean
Operators
 if-else
 switch-case
 for loop
 while loop
 Examples


Priority of Math Operators
Priority
High
Med
Low

Operator
Multiplication *
Division /
Residue %
Addition +
Subtraction -

Example
1 + 4 / 2 = 3
3 * 5 % 2 + 1 = 2
1 + 2 * 3 = 7

Parentheses change the priority.
Example
int a = 1,
b = 2,
c = 3;
int res1 = a + b * c;
// a + 6
//
7
int res2 = (a + b) * c;
//
3 * c
//
9


Variable Type Change (Math Operation)
Assume the following:
int a1 = 1, a2 = 2, a3 = 3;
float b1 = 0.1, b2 = 0.2, b3 = 0.3;

 In a math operation of the same type of variables:
(a1 + a2) * a3 // this would be of type int
b1 * b2 / b3 // this would be of type float

 In a math operation of the different types of variables:
(a1 + b1) * a3 // this would be of type float
b3 * a2 / b2 // this would be of type float

The result would have the type of the most precise variable or the
variable with the widest range.


Variable Type Change (Assignment)
 Assignment of same type (left and right side):
int a1 = 1, a2 = 2, a3 = 3;
float b1 = 0.1, b2 = 0.2, b3 = 0.3;
int a_res;
float b_res;
a_res = (a1 + a2) * a3; // a_res = 9
b_res = b1 * a2 / b3; // b_res = 0.66...

 Assignment of different type (left and right side):
a_res = (a1 + b2) * a3; // righ side loses its decimal
b_res = a1 * a2 * a3; // b_res = 6

Note 1: Literals have “Data Type” too.
Note 2: It is possible to change the type of a variable temporarily
by casting:
b_res = (float) a1 / a2; // cast a1 to float before division


Variable Type Change (Example)
Suppose:
int a1 = 1, a2 = 2, a_res;
float b1 = 0.1, b2 = 0.2, b_res;

Indicate the value of the left hand side variable after assignment:
1

a_res = a1 * a2;

2

b_res = a1 * a2;

3

a_res = a1 / a2;

4

b_res = a1 / a2;

5

a_res = a1 / 3;

6

b_res = a1 / 3.0;

7

a_res = (float)a1 / a2;

8

b_res = (float)a1 / a2;

9

a_res = (int)b2 / b1;

10 b_res = (int)b2 / b1;

11 a_res = (int)(b2 / b1);

12 b_res = (int)(b2 / b1);

13 a_res = b2 / b1;

14 b_res = (float)(b1 / b2);


Relational Operators
Usually used in if or while
Sign
>
>=
<
<=
==
!=

Description
Greater than
Greater than or equal
Less than
Less than or equal
Equal
Not equal

Example
if (a > b)
while (a <= b)
if (a == b)
while (a != b)

The result of any relational operation (such as a == b) would be
true (1) or false (0)
Boolean
Note: Do not confuse == (equality) with = (variable assignment).


Boolean Operators
Again they are usually used in if or while
||
&&
!

OR
AND
Not

if (a1 > b1 || a2 > b2)
if (a1 > b1 && a2 > b2)
if !(a > b)


if-else
if could be accompanied by an else but it’s not necessary.

Do not forget the braces if necessary (when there is more than one
command).
Example:
float a;
cin >> a;
if (a >
cout
else
{
a *=
cout
}

1)
<< "it's greater than 1.";
2; // a = a * 2;
<< a;


More on Equality (==)
Equal real numbers?

tolerance (eg. ± 0.1)

There are no two equal real values in reality, there is always a
tolerance for the accuracy of equality of two real numbers.
float a;
cin >> a;
if (a == 1.5) // Bad code !
cout << "1.5";
if (a < 1.6 && a > 1.4) // Good code !
cout << "Close enough to 1.5";
if (fabs(a – 1.5) < 0.1) // Good code !
cout << "Close enough to 1.5";


switch-case
int a;
cin >> a;
switch(a)
{
case 1:
cout << "one";
break;
case 2:
cout << "two";
break;
case 3:
cout << "three";
break;
}

Do not forget break and colon (:) after each case.
Note: any switch-case could also be implemented using if-else.


switch-case Replaced by if-else
int a;
cin >> a;
if(a == 1)
cout << "one";
else if(a == 2)
cout << "two";
else if(a == 3)
cout << "three";

This code seems neater when written using switch-case
especially when there are multiple cases.


for loop
We use it when a similar task should be performed more than once
(usually for a known number of iterations).
The common syntax of for loop is:
for (int c = 0; c < n; c++)
{
// The loop-counter(c) should be of
// type integer (long, short, etc).
// This loop runs for n iterations.
// In the first iteration c is 0.
// In the last iteration c is n-1.
}


for loop (Example)
Implement a code to print the 10 times table on the screen.


while loop
Like the for loop we use it when a similar task should be performed
more than once (usually for an unknown number of iterations).

1)

while (a > 0)
{
// do this
}

do
{

2)

// this
}
while (a > 0);

Example:
int a;
do
{
cout << "Enter a positive integer: ";
cin >> a;
}
while (a > 0);
cout << "Game over! n";


Example
1. Write a code to ask the user two numbers (one real and one
whole). Then prints the result of the first number to the power of
the second number.

2. Modify the program so that it keeps doing part1, until the user
enters 0 for both numbers.


MECH-215 TA
C++ Programming
Session #4
Feb 06 2013
Tutor: Pooya Merat

P. Merat Feb 06 2013

MECH-215 TA
Topics:





More on for loop
for loop vs. while loop
In-Class Exercise
Home Exercise


More on for loop
int i;
for (i = 5; i < 7; i++)
{
cout << i;
}
cout << "Loop Finished" << i;

Step 1: i = 5; then go to Step 2
Step 2: if i < 7 is true go to Step 3, otherwise exit the loop
Step 3: cout << i; then go to Step 4
Step 4: i++; then go back to Step 2
So at the end, value of i would be 7.


More on for loop (Example)
What would be printed on the screen in the following codes?

1

2

3

int i;
for (i = 5; i < 4; i++)
{
cout << i;
}
for (int i = 5; i <= 8; i++)
{
cout << i;
}
int i;
for (i = 8; i > 5; i--)
{
cout << i;
}


More on for loop (Example)
What would be printed on the screen in the following codes?

4

5

int i;
for (i = 5; i > 4; i++)
{
cout << i;
}
int i;
for (i = 2; i < 7; i = i+2)
{
cout << i;
}


for loop vs. while loop
In general there’s more flexibility with while loop, but they could be
used interchangeably.

1

2

3

for (int i = 5; i < 8; i++)
{
cout << i;
}
int i = 5;
while (i < 8)
{
cout << i++;
}
int i = 5;
do
{
cout << i++;
}
while (i < 8);


In-Class Exercise
Write a code which gets two integer numbers from the user, and
prints all the integers from the first integer to the second integer.
Sample behavior (All the red characters are the user input, the rest
is program output):
S = 5
E = 7
S to E : 5, 6, 7,
OR

Write the Code with:
1. for loop
2. while loop
3. do-while loop

S = 9
E = 6
S to E : 9, 8, 7, 6,


Home Exercise
Implement a program to perform the length unit conversion.
[m(meter), f(foot), k(kilometer), M(miles)]
Sample behavior (All the red characters are the user input, the rest
is program output):
Length : 50 m f
~= 166.667 f

[ 1.0 foot = 0.3 m

,

1.0 mile = 1.6 km ]


Home Exercise (Hint)
Let’s name things:
Length : 51 m f
In this example:
 The first unit (m) : The Origin Unit
 The second unit (f) : The Destination Unit
Hint:
One way is to break the problem into two completely separate
problems:
1.
First Convert the Origin Unit to a Standard Unit
(Regardless of the Destination Unit)
2.

Then Convert the Standard Unit to the Destination Unit.


MECH-215 TA
C++ Programming
Session #5
Feb 27 2013
Tutor: Pooya Merat


MECH-215 TA
Topics:
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

Library Functions
Functions Prototype
Function Output
Function Input(s)
Local Variable
Reference
Examples

 Quiz Answer
 Indentations


Library Functions
#include <iostream>
using namespace std;
#include <cmath>
int main()
{
cout << sin(0.2);
cout << sqrt(3);
return 0 ;
}

Note: An output is returned after the sin and sqrt is been called.


Function Prototype
It’s the function identity information:

1) Name
2) Number and type(s) of input argument(s)
3) Type of output (if any)


Function Prototype (Example)
A function name is an identifier and should obey the naming rules
(should consists of only letters and numbers and underscore).
int my_iadd (int, int)

int my_imax2 (int, int)

double my_dadd (double, double) int my_imax3 (int, int, int)
float my_fadd (float, float)

float my_fmax2 (float, float)

double my_power (float,
unsigned int)

void my_print (string)

void my_hello ()
void my_hello (void)

double my_dmin7 (double,
double,
double,
double,
double,
double,
double)

What is the prototype of sin function ?


Function Output
in C++ any function can only have one or no output.
No output:
void my_print (string)

void my_HelloWorld ()
{

void my_HelloWorld ()

cout << "Hello World!"
<< endl;

Using void is necessary.
No need for return at the end.

}

One output:

int my_iadd (int a, int b)

int my_iadd (int, int)

{
return a + b ;

Must have return at the end.

}


Function Input(s)
Any function can have any number of inputs.
No input:
void my_hello ()

void my_hello (void)

int blah ()

int blah (void)

One or more inputs:
int my_imax3 (int, int, int)
void my_print_power (float, unsigned int)


Local Variables
main Function
int main ()
{

my_iadd Function
int my_iadd (int a, int b)
{

int X, Y; cin >> X >> Y;

cout << X << Y;

cout << my_iadd(X, Y);
cout << a << b;

return a + b ;
}

return 0;
}

Whenever a function is called, all its local variables are declared
locally and just after the function execution, all those local variables
are removed from memory and de-allocated (except the static
variables).


Reference (&)
main Function
int main ()
{
int X, Y; cin >> X >> Y;
int res;

my_iadd Function
void my_iadd2 (int a,
int b,
int & c)
{
c = a + b ;

my_iadd2 (X, Y, res);
cout << res;

}

return 0;
}


Example
What’s the output of this program?
#include <iostream>
void f1 (double a, int b, double Res)
{
Res = 1;
for (int i = 0; i < b; i++)
Res *= a;
}
int main()
{
double res;
f1 (5, 2, res);
cout << res;
return 0 ;
}

Why the result is not as expected?

Practice
Write a function to get two variables from the user and send them
back to the main function.
Solution:
#include <iostream>
void GetTwoNum (int & first, int & second)
{
cout << "enter first num: "; cin >> first;
cout << "enter second num: "; cin >> second;
}
int main()
{
int a, b;
GetTwoNum (a, b); // function call
cout << "first one is: " << a
<< " and second is: " << b << endl;
return 0 ;
}

Quiz Answer
#include <iostream>
int main()
{
for (int X = 0; X <= 100; X++)
for (int Y = 0; Y <= 100; Y++)
if (Y*100 + X - 5 == 2*(X*100 + Y))
cout << "X = " << X << " and Y = " << Y << endl;
return 0 ;
}


Respect the Indentations Rule Please!
There are many Indentation standards.
Allman standard:
#include <iostream>

Readable Code

int main()
{
for (int X = 0; X <= 100; X++)
{
for (int Y = 0; Y <= 100; Y++)
{
if (Y*100 + X - 5 == 2*(X*100 + Y))
{
}
}
}
return 0 ;
}


Terrible Indentations
#include <iostream>
int main() {
for (int X = 0; X <= 100; X++) {
for (int Y = 0; Y <= 100; Y++) {
if (Y*100 + X - 5 == 2*(X*100 + Y))
}
}
return 0 ;
}

Indentations:
 Make your code more readable, even for yourself.
 And result in better comprehension and less errors.

MECH-215 TA
C++ Programming
Session #6
March 06 2013
Tutor: Pooya Merat

P. Merat March 06 2013

MECH-215 TA
Topics:
Functions and:
 Global Variables
 Static Variables
 Structures
 Practice


Functions Interactions with outside
There are several ways for functions to access or pass a value
outside.
Ways that a function can access a foreign variable:
 Through its input arguments
 Global variables
…
Ways that a function can affect a variable outside:





Through its output (return)
Call by reference (&)
Global variables
...


Global Variables
#include <iostream>
int cnt = 0;
void increase(void)
{
cout << "++" << endl;
cnt ++;
}
int main()
{
for (int i = 0; i < 5; i++)
increase();
cout << cnt << " Bye!" << endl;
return 0;
}


Static Variables
#include <iostream>
int increase(void)
{
static int cnt = 0;
cout << "++" << endl;
cnt ++;
return cnt;
}
int main()
{
int C;
for (int i = 0; i < 5; i++)
C = increase();
cout << C;
return 0;
}


Functions and Structures
#include <iostream>
#include <string>
struct student_type
{
string name;
int age;
int ID;
double GPA;
};
student_type get_student()
{
student_type st;
cout << " Enter name:
cout << " Enter age:
cout << "
Enter ID:
cout << " Enter GPA:

";
";
";
";

cin
cin
cin
cin

>>
>>
>>
>>

st.name;
st.age;
st.ID;
st.GPA;

return st;
}
void Get_student(student_type
{
cout << " Enter name: ";
cout << " Enter age: ";
cout << "
Enter ID: ";
cout << " Enter GPA: ";
}

& s) // Reference
cin
cin
cin
cin

>>
>>
>>
>>

s.name;
s.age;
s.ID;
s.GPA;


void disp_student(student_type s)
{
cout << "Name: " << s.name << endl;
cout << " Age: " << s.age << endl;
cout << " ID: " << s.ID << endl;
cout << " GPA: " << s.GPA << endl;
}
student_type find_best_GPA(student_type st1,
student_type st2,
student_type st3)
{
if (st1.GPA >= st2.GPA && st1.GPA >= st3.GPA)
return st1;
if (st2.GPA >= st1.GPA && st2.GPA >= st3.GPA)
return st2;
return st3;
}
int main()
{
student_type student_1, student_2, student_3;
cout << "First student:" << endl;
student_1 = get_student();
cout << "Second student:" << endl;
student_2 = get_student();
cout << "Third student:" << endl;
Get_student(student_3); // Call by Reference
student_type student_best_GPA;
student_best_GPA = find_best_GPA(student_1,
student_2,
student_3);
cout << "Following has the highest GPA:" << endl;
disp_student(student_best_GPA);
return 0;
}


Practice
Write a Calculator program,
Step 1 : Which gets two operands and one operator ( + - )
Sample behavior:
User Input >> 2 + 5
Program output >> 7

To get the user input, use this code:
cin >> Operand_1 >> Operator >> Operand_2 ;

Step 2 : Write a separate function for each of the operations.
Operation_X (Operand_1, Operand_2)

Step 3 : Extend the calculator to accept these operators: * / ^
and write the corresponding functions.
Step 4 : Program keeps getting the user inputs, until user enters 0 as
the operator.

Practice (Solution)
Solution to Step1 and Step2:
#include <iostream>
double ADD(double a, double b)
{
double Ans = a + b;
return Ans;
}
void SUB (double & A, double a, double b)
{
A = a - b;
}
void MUL(double a, double b)
{
cout << a * b;
}
double DIV(double a, double b)
{
return a / b;
}


int main()
{
cout << "Welcome to My Calculator!" << endl;
double o1, o2, ans;
char sign;
cin >> o1 >> sign >> o2;
switch (sign)
{
case '+':
ans = ADD(o1,o2);
cout << ans;
break;
case '-':
SUB(ans, o1, o2);
cout << ans;
break;
case '*':
MUL(o1, o2);
break;
case '/':
ans = DIV(o1, o2);
cout << ans;
break;
}
return 0;
}


MECH-215 TA
C++ Programming
Session #7
March 13 2013
Tutor: Pooya Merat


MECH-215 TA
Topics:
Recursion
 Examples and Practice


Recursion Example 1
𝐹 (0) = 1

Base case

𝐹 ( 𝑛) = 𝑛 ∗ 𝐹 ( 𝑛 − 1)

Recursive formula

int f(int n) // Recursive
{
if (n == 0) // Base case
return 1;
return n * f(n - 1); // Recursive formula
}
int f(int n) // Explicit
{
int res;
for ( int i = 0 ; i <= n ; i++ )
res *= i;
return res;
}


Recursion Example 2
𝐹 (0) = 0

Base case

𝐹 ( 𝑛) = 𝑛 + 𝐹 ( 𝑛 − 1)

Recursive formula

int f(int n) // Recursive
{
// You write the “base case” here to stop the recursion
return n + f(n - 1);
}
{
int res = 0;
for ( int i = 0 ; i <= n ; i++ )
res += i;
return res;
}
{
return (n * (n - 1)) / 2;
}


Order of Recursion (1)
void f1(int num)
{
if (num == 0)
return;
cout << num;
f1(num - 1);
}

f1 (4)
cout << 4
f1 (3)
cout << 3
f1 (2)
cout << 2
f1 (1)
cout << 1
f1 (0)
Recursion ends here


Order of Recursion (2)
void f2(int num)
{
if (num == 0)
return;
f1(num - 1);
cout << num;
}

f2 (4)
f2 (3)
f2 (2)
f2 (1)
f2 (0)
Recursion ends here
cout << 1
cout << 2
cout << 3
cout << 4


Recursion Example 3
void print_star(int n)
{
if ( n == 1 )
cout << "*" << endl;
else
{
print_star(n-1);
for ( int i = 1 ; i <= n ; i++ )
cout << "*" ;
cout << endl;
}
}

The output of this function would look like: (1 or 2 ?)

1

*
**
***
****
*****
******
*******
********

2

********
*******
******
*****
****
***
**
*


Towers of Hanoi (1)
1

2

3

1

2

3

1

2

3

1

2

3

Top Disk
Base Disk

In this example:
Rod #1: Origin
Rod #2: Temporary
Rod #3: Destination


Towers of Hanoi (2)
1

2

3

1

2

3

1

2

3

1

2

3

Top Disks
Base Disk

void hanoi(int n, int org, int des, int temp)
{
// You write the “base case” here to stop the recursion
hanoi_tower(n-1, org, temp, des);
cout << org << " to " << des << endl; // Base move
hanoi_tower(n-1, temp, des, org);
}

Practice
1.
Write the Greatest Common Devisor function using the
following recursive formula:
𝒙
𝒈𝒄𝒅( 𝒙, 𝒚) = { 𝒈𝒄𝒅(𝒚 , 𝒓𝒆𝒎𝒂𝒊𝒏𝒅𝒆𝒓(𝒙, 𝒚))

𝒊𝒇 𝒚 = 𝟎
𝒊𝒇 𝒚 > 𝟎

2.
Write the Hanoi function using the following recursive formula:
(The optimal number of movements)
𝟏
𝒉𝒂𝒏𝒐𝒊( 𝒏) = {
𝟐 ∗ 𝒉𝒂𝒏𝒐𝒊( 𝒏 − 𝟏) + 𝟏

𝒊𝒇 𝒏 = 𝟏
𝒊𝒇 𝒏 > 𝟏


MECH-215 TA
C++ Programming
Session #8
March 27 2013
Tutor: Pooya Merat


MECH-215 TA
Topics:
Arrays





Intro.
Passing Arrays to Functions
Multi-Dimensional Arrays
Examples


Arrays
Usually a long series of similar data (of any type).
Usually accompanied with a for loop.
Array >> A series of data
for loop >> doing similar task on a series of data

C++ Definition:
int a[10]; // an array capable of storing 10 integer numbers
Array index

0

1

8

9

Value

4

3

2

8

150

154

182

186

Memory
Address

Note: Never try to access (or assign a value to) out of arrays
boundaries.(for the example above: a[20], a[10] or a[-6])


Array Example 1
Get 7 students’ GPAs and store them in an array. Then print out the
average, maximum and minimum GPAs.
float GPA[7];
for (int i = 0; i < 7; i++)
{
cout << "Enter GPA #" << i+1 << ": ";
cin >> GPA[i];
}
float sum = 0, max = GPA[0], min = GPA[0];
for (int i = 0; i < 7; i++)
{
sum += GPA[i];
if (GPA[i] > max)
max = GPA[i];
if (GPA[i] < min)
min = GPA[i];
}
cout << "Average is: " << sum/7.0 << endl
<< "max is: " << max
<< " and min is: " << min << endl;


Passing Arrays to Functions
 Always the array address is sent to the function, like the call by
reference.
 When calling the function only the name to the array should be
included.
 When declaring the function (or in function prototype) array name
should come with brackets (empty or with proper size).
o If array is more than one dimension, size of higher
dimensions must be mentioned in the function input
declaration.
 The length of the data in the array should be sent if it’s unknown
to the function.
Example:
float Array_fun (float a[], int arr_len) {} // declaring
Array_fun (A, size); // calling


Multi-Dimensional Arrays
Declaration:
int A[][] = {{1,2,3},{4,5,6}};
int A[][2][2] = { {{1,2},{3,4}} , {{5,6},{7,8}} };

Note: In multi-dimensional arrays only the first dimension could be
left empty, in definition or in function parameters.
Usually the proper number of nested loops should be used to do an
operation on the array.
Another way to initialize:
int A[2][2][2] = {1, 2, 3, 4, 5, 6, 7, 8};


Matrices Multiplication
5
6

7

5

7×5

5×6

7×6


Practice 1
Write a code to get two matrices (2 x 2) from the user and prints out
their addition and multiplication.

Next step: write two functions for aforementioned operations.


Practice 2
3-D Matrices
Write a program to print out an arbitrary 2x2x2 matrix.
First print out the orange data, then blue, red and green.
Dim 2

Dim 1

Dim 3


Practice 3
1) Write a code that calculates the end-effector position of a planar
(2D) robotic manipulator.
>> Use arrays to store the joint angles and link lengths.
Here is the formula for a three link (2-DOF) manipulator:
𝑥 = 𝐿1 cos(𝜃1 ) + 𝐿2 cos(𝜃1 + 𝜃2 )
+ 𝐿3 cos(𝜃1 + 𝜃2 + 𝜃3 ) + ⋯
𝑦 = 𝐿1 sin(𝜃1 ) + 𝐿2 sin(𝜃1 + 𝜃2 )
+ 𝐿3 sin(𝜃1 + 𝜃2 + 𝜃3 ) + ⋯
2) Use an structure array to store
data.

(x,y)
Link 2

Joint 1

y

Link 1

L1
θ1

x


L2

θ2

Joint 2

MECH-215 TA
C++ Programming
Session #9
April 03 2013
Tutor: Pooya Merat

P. Merat April 03 2013

MECH-215 TA
Topics:
Pointers and





Arrays
Strings
Functions
Structures

 Dynamic Memory Allocation


Pointers Intro.
C(++) Operators:
&a

The address of variable a in memory

* b

The data in the address stored in a

int a = 10;
int * a_addr = & a; // declaration and initialization of
// the pointer to a

a
10
2555228

a_addr
2555228
14285484


Pointer Example
int a;
int * a_addr; // declare a pointer asterisk sign must be used.
a_addr = & a; // Equate a_addr with the address of a.
a = 20;
cout << a;
*a_addr = 30;
cout << a; // What will be the output?


Pointer Common Mistakes
int * a_addr;
a_addr = 20; // There’s no point in doing so, because you do
// not know what is in the memory address of 20.
& a_addr = 20; // Invalid command. You cannot change the
// address of an existing variable.

Note: Pointer type must agree with the type of variable it points to.
float a;
int * a_addr;
a_addr = &a;


Pointers and Functions
#include <iostream>
void f (int * a1, int * a2)
{
// swap a1 and a2
int temp = * a1;
* a1 = * a2;
* a2 = temp;
}
int main()
{
int v1 = 3, v2 = 20;
f (& v1, & v2);
cout << v1 << endl << v2 << endl;
system("pause");
return 0;
}


Pointers and Functions Example
Find the errors in this code:
void f(int * a1, int & a2)
{
// swap a1 and a2
int temp = a1;
a1 = a2;
a2 = temp;
return 0;
}
int main()
{
int v1 = 3, v2 = 20, v3;
v3 = f(v1, v2);
system("pause");
return 0;


}

Pointers and Functions Example
Here is the corrected code:
void f(int * a1, int & a2)
{
// swap a1 and a2
int temp = *a1; <<<<<< int temp = a1;
*a1 = a2; <<<<<< a1 = a2;
a2 = temp;
}
int main()
{
int v1 = 3, v2 = 20, v3;
f(& v1, v2); <<<<<< v3 = f(v1, v2);
return 0;
}


Pointers and Arrays
Arrays in fact use pointers.
When you write:
int a[5] = {1,2,3,4,5};

1
2555228

2

3
a
2555228
14285484

a will contain the address of the first element of the array.
You can also write:
int * a = {1,2,3,4,5};


Pointers and Arrays (cont.)
int a[5] = {1,2,3,4,5};
cout << a[2]; // prints 3, the third element of the array.
cout << * (a + 2); // prints 3 again, since a is a pointer.
cout << * a; // prints 1.
cout << a[0]; // prints 1, again.
cout << a; // Address of the first element
cout << & a; // Address of a, refer to the last figure.

So when you declare an array:
 First, your computer reserves enough memory for the data of
that array.
 Second, a pointer to the first element of the array will be created
with the declared name and type.

Pointers, Arrays and Functions
void print_array_1(int a[], int len)
{
for (int i = 0; i < len; i ++)
cout << *(a + i) << 't'; // or cout << a[i]
cout << endl;
}
void print_array_2(int * a, int len)
{
for (int i = 0; i < len; i ++)
cout << a[i] << 't'; // or cout << *(a + i)
cout << endl;
}
int main()
{
int A[] = {1,2,3,4,5};
print_array_1(A, 5); // or print_array_2(A, 5);
return 0;
}


Pointers and Strings
Strings are arrays with two main characteristics:
1.
2.

String type is a char array and is intended to store text.
The last character should be the Null character: '0'

char s1[] = "Hi!";
char s1[3] = "Hi!";
char s3[4] = {'H','i','!','0'};
char * s2 = "Hi!";
string s4 = "Hi!"; // Requires #include <string>.

Note: double quote sign ( " ) must be used for strings, and single
quote sign ( ' ) for characters.

Pointers and Strings (cont.)
Because of the existence of the Null character at the end, when
passing string to functions, there is no need to send the length of the
string unlike when passing arrays to function.
Some library functions (do not forget to include <string>):
 strlen(string) : returns the length of string without '0'.
char * s1 = "Good";
cout << strlen(s1); // Prints 4.

 strcmp(string, string): compares two strings, returns 0 on equality.
char s1[] = "Hi !";
char s2[5] = {'H','i',' ','!','0'};
if (strcmp(s1, s2))
cout << "Different";
else
cout << "Same"; // strcmp(s1, s1) returns 0


Pointers and Strings (Example 1)
Let’s write our own strlen function:
int my_strlen_1(char s[])
{
int i = 0;
while(s[i++] != '0');
return i-1;
}

Another version (with an error, find it!):
int my_strlen_2(char s[])
{
for(int i = 0; *(s+i) != '0'; i++);
return i;
}


Pointers and Strings (Example 2)
Now let’s write our own function for comparing two strings:
bool my_strcmp(char *s1, char s2[])
{
bool equal = true;
int i = 0;
while(s1[i] != '0' && *(s2 + i) != '0')
if ( *(s1 + i) != s2[i++])
equal = false;
return equal; // Note that unlike strcmp this function
// returns true when strings are equal.
}

However:
char s1[] = "C+";
char s2[] = "C++";
cout << my_strcmp(s1, s2); // Prints 1 !

Why ?


Pointers to Structures
To access structure pointer field use:
struct_pointer -> field_name NOT *struct_pointer.field_name
struct Contact_t
{
string Name;
string Email;
};
void Get_Contact(Contact_t * c)
{
cout << "Enter Name: "; cin >> c -> Name;
cout << "Enter Email: "; cin >> c -> Email;
}
int main()
{
Contact_t Contact_List[50];
for (int i = 0; i < 50; i++)
Get_Contact(&Contact_List[i]);
return 0;
}


Dynamic Memory Allocation
For declaring dynamic variables during program execution.
1. First declare a regular pointer named dyn_pointer:
int * dyn_pointer; // pointer

2. Allocate an integer with an initial value of 5 to a memory
address and put that address in dyn_pointer.
The address will be reserved for this variable.
dyn_pointer = new int (5);

3. When you are done with the array, release its address in
memory:
delete dyn_pointer;


Dynamic Memory Allocation (cont.)
These are similar procedure for the dynamic allocation of an array:
int * dyn_pointer_arr; // Declare a pointer with proper type
dyn_pointer_arr = new int [50]; // reserve an array of length
// 50 and set dyn_pointer_arr to the
// address of the first element.
delete [] dyn_pointer_arr; // Release the array memory.


MECH-215 TA
C++ Programming
Session #10
April 10 2013
Tutor: Pooya Merat


MECH-215 TA
Topics:
Classes:






Constructor (Default, Overloaded)
Static Variables in Classes
Destructor
Operator Overloading
Friend Functions


Classes
Syntax: (They are very similar to structures)
class my_class
{
private:
// Usually variables
int var;
public: // Everything after this line will be public
// Usually functions >> methods
int method_1(void);
};

my_class would be like a data type after its declaration:
my_class a , b;

a and b are objects of this class.
Using dot (.) operator (only) public methods and data members of the
object would be accessible:
cout << a.method_1();
cout << a.var;//var is not accessible outside my_class methods

Classes (Example)
class my_class
{
private:
int var;
public:
int get_var(void) // Accessor method
{
return var;
}
void set_var(int x) // Mutator method
{
var = x;
}
};
int main()
{
my_class a;
a.set_var(10);
cout << a.get_var();
return 0;

Note that both functions
(methods) already have
access to var.
There is no need to pass
any class data to methods.

}


Declaring Methods outside the Class
class my_class
{
private:
int var;
public:
int get_var(void); // Method protype
void set_var(int); // Method protype
};
int my_class::get_var(void) // my_class Accessor method
{
return var;
}
void my_class::set_var(int x) // my_class Mutator method
{
var = x;
}

Note the :: operator between class name and method name.


Class Common Mistake
class my_class
{
private:
int var;
public:
int get_var(void); // Method protype
void set_var(int); // Method protype
};
...
my_class a;
...

When accessing a class entity the (::) operator must be used and
when accessing an object entity dot (.) must be used.
a.set_var
my_class::get_var

There is no something like:
my_class.set_var
a::get_var


Class Default Constructors
To initialize an object to some default values.
class my_class
{
private:
int var; // var cannot be initialized here.
public:
my_class() // Default Constructor
Constructor should
{
have the exact same
var = 10;
name as the class.
}
};
Now whenever an object of my_class is declared its var would be 10

by default.
my_class a, b, c;

Note: Constructor has to be public.


Overloading
Overloading: Multiple declaration of the same thing.
Function overloading:
int my_add(int a, int b) // First version
{
return a + b;
}
int my_add(int a, int b, int c) // Second version
{
return a + b + c;
}
double my_add(double a, double b, double c) // Third version
{
return a + b + c;
}
int main()
{
cout << my_add(1,2) << endl // First version will be called
<< my_add(1,2,3) << endl // Second version
<< my_add(0.1,0.2,0.3); // Third version
return 0;
}

Class Constructor Overloading
class my_class
{
private:
int var1, var2;
public:
my_class()
{
cout << "Default Constructor" << endl;
var1 = 10; var2 = 20; // Initialize to default.
}
my_class(int x)
{
cout << "First Overloaded Constructor" << endl;
var1 = x; var2 = 20; // Initialize only the first var.
}
my_class(int x, int y)
{
cout << "Second Overloaded Constructor" << endl;
var1 = x; var2 = y; // Initialize both vars.
}
// Other Methods ...
};


Declaration (in the main function for example):
my_class a1, // First constructor will be called automatically
a2(5), // Second constructor will be called
a3(5,10); // Third constructor

There is no need to call the constructors manually, and you must not
do that!


Forward Declaration
It is possible to declare functions or classes after they are used, but
their prototypes must be written before they are used.
void Hello();
class my_class;
int main()
{
Hello();
my_class a;
cout << a.method_1();
return 0;
}
void Hello()
{
cout << "Hello!";
}
class my_class
{
// my_class declaration
};

Scope
In C(++), blocks show different levels of program.
 Every function, if, for ,while, structure or class has a block.
 It is possible to declare most data-types (int, array, string, …)
inside any block, but the data lifetime is limited to that block and
after the block it does not exist (except static or ...).
 Every block has access to its parent blocks data and not to its
sub-blocks data.
// Global scope (everything which is not in any block)
int c; // Global variable
int my_add(int a, int b) // Global function
{ return a + b; }
int main()
{ // main function scope
if (...)
{ // if scope
}
return 0;
}

Static Variables
In functions:
int increase(void)
{
static int cnt = 0; // It initializes only once
cout << "++" << endl;
cnt ++;
return cnt;
} // cnt never de-allocates (but
// only increase function can access it).

But in classes:
static keyword for data members of a class represents a shared
data between all the objects of that class.


Static Variables in Classes
class my_class
{
private:
int private_var;
public:
static int shared_var; // It should be public
};
int my_class::shared_var
// class
int main()
{
my_class a, b;
cout << a.shared_var;
b.shared_var ++;
cout << a.shared_var;

= 5; // Note: accessing the
member not an object member

// Will print 5
// Will print 6

return 0;
}

In this example there are 2 copies of private_variable, but only
one shared_variable is declared.

Destructor
Is called when an object of a class is about to be de-allocated. Might be
useful to count the number of objects of a class.
class my_class{
public:
static int num_obj; // Shared data
my_class() // Constructor method
{
cout << "an object just Constructed!";
num_obj++;
}
~ my_class() // Destructor method
Destructor should
{
cout << "an object just Destructed!";
num_obj--;
have the exact same
}
name as the class:
};
int my_class::num_obj = 0;
~class_name
int main()
{
{
my_class a, b;
cout << my_class::num_obj; // Prints 2
}
cout << my_class::num_obj << b.num_obj; // Prints 0 and 0
return 0;
}


Operator Overloading
Class = Class + Class
class my_class
{
public:
int var;
my_class(){ var = 10; }
my_class operator+(my_class x)
{
my_class res;
res.var = var + x.var;
return res;
}
};
int main()
{
my_class a, b, c;
c = a + b;
// or c = a.operator+(b);
cout << c.var; // Will print 20
return 0;
}


Operator Overloading (cont.)
These are the operators that could be overloaded in classes.
(Overloadable operators)
+

-

*

/

=

<

>

+=

-=

*=

/=

<<

>>

<<=

>>=

==

!=

<=

>=

++

--

%

&

^

!

|

~

&=

^=

|=

&&

||

%=

[]

()

,

->*

->

new

delete

new[]

delete[]


Friend Functions in Class
Using a friend keyword before a function prototype, that function
will become friendly to all the members of the class.
class my_class
{
int var1, var2; // private members
public:
my_class(){ var1 = 10; var2 = 20;}
friend void read_my_class_vars(my_class);
...
};

Not a method!

void read_my_class_vars(my_class x) // input type is my_class
{
cout << x.var1 + x.var2; // var1,2 are private members !!
}
int main()
{
my_class a;
read_my_class_vars(a); // if it was method: a.read_my...();
return 0;
}


Friendship between Classes
class class_1
{
int var1, var2; // private members
public:
friend class class_2;
...
};

Since class_1 declared class_2 as a friend; methods of class_2
have access to all class_1 private members.
class class_2
{
int var1, var2;
public:
void read_class_1(class_1 x)
{
cout << x.var1 + x.var2;
}
...
};


Usage in main function:
int main()
{
class_1 a;
class_2 b;
b.read_class_1(a);
return 0;
}

Note: Class friendships are not necessarily two-way relationships!


Final Note
You can use the struct keyword instead of class, but unlike class,
the default member type in struct is public.
struct my_class // using structure instead of class keyword
{
public: // this keyword is not necessary
int var;
my_class(){ var = 10; }
my_class operator+(my_class x)
{
my_class res;
res.var = var + x.var;
return res;
}
};
int main()
{
my_class a, b, c;
c = a + b;
// or c = a.operator+(b);
cout << c.var; // Will print 20
return 0;
}

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