C++ Basics

C++ Basics
Inam Ul Haq
Lecturer in Computer Science
University of Education Okara Campus
inam@ue.edu.pk, inam.bth@gmail.com
Subject: Programming Language for Mathematics
Class: BS(Hons) Mathematics

Header Files
// header files are preprocessor directives that are included to call built-in
functions to be used in the program
// e.g. for keywords: cin and cout, the header file iostream.h is used
#include <iostream.h>
Void main() {
//variable declaration
//read values input from user
//computation and print output to user
return 0;
}
Note: After you write a C++ program you compile it; that is, you run a
program called compiler that checks whether the program follows the C++
syntax:
• if it finds errors, it lists them
• If there are no errors, it translates the C++ program into a program in machine
language which you can execute
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Notes
• // is used for comments (this is not executed)
• indentation is for the convenience of the reader; compiler ignores all spaces and new line ;
the delimiter for the compiler is the semicolon
• E.g.
• Void main()
• {
• Clrscr();
• Int a,b;
• If(a==b)
• {
• Cout<<“a is equal to b”<<endl;
• all statements ended by semicolon
• Lower vs. upper case matters!!
• Void is different than void
• Main is different that main
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Hello world program
When learning a new language, the first program people
usually write is one that salutes the world :)
Here is the Hello world program in C++.
Void main() {
cout << “Hello world!”;
getch();
}
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Variable declaration
Syntax: <variable-name> <type>
e.g:
• int n, average; //integer
• Double m; //real number
• char c, my-character//character
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Input statements
cin >> variable-name;
Meaning: read the value of the variable called <variable-
name> from the user
Example:
cin >> a;
cin >> b >> c;
cin >> x;
cin >> my-character;
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Output statements
cout << variable-name;
Meaning: print the value of variable <variable-name> to the user
cout << “any message “;
Meaning: print the message within quotes to the user
cout << endl;
Meaning: print a new line
Example:
cout << a;
cout << b << c;
cout << “This is my character: “ << my-character << “ he he he”
<< endl;
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If statements
if (condition) {
S1;
}
else {
S2;
}
S3;
condition
S1 S2
S3
True False
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Boolean conditions
..are built using
• Comparison operators
== equal
!= not equal
< less than
> greater than
<= less than or equal
>= greater than or equal
• Boolean operators
&& and
|| or
! not
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Examples
Assume we declared the following variables:
int a = 2, b=5, c=10;
Here are some examples of boolean conditions we can
use:
• if (a == b) …
• if (a != b) …
• if (a <= b+c) …
• if(a <= b) && (b <= c) …
• if !((a < b) && (b<c)) …
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If Statement
void main() {
int a,b,c;
cin >> a >> b >> c;
if (a <=b) {
cout << “min is “ << a << endl;
}
else {
cout << “ min is “ << b << endl;
}
cout << “happy now?” << endl;
}
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While Loop
while (condition) {
S1;
}
S2;
condition
S1
S2
True False
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While example
//read 100 numbers from the user and output their sum
void main() {
int i, sum, x;
sum=0;
i=1;
while (i <= 100) {
cin >> x;
sum = sum + x;
i = i+1;
}
cout << “sum is “ << sum << endl;
}
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For Loop
• for ( initialization; conidition; increment/decrement)
• {
• Statement 1’
• Statement 2;
}
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For Loop Example
• #include <iostream>
• int main ()
• {
• for( int a = 10; a < 20; a = a + 1 )
• {
• cout << "value of a: " << a << endl;
• }
• return 0;
• }
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Do While Loop
• do
{
block of code;
statement 1;
statement 2;
}
while (condition); //it is called test condition
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Do While Loop Example
• #include <iostream>
• #include <conio.h>
• int main ()
• {
• int a = 10;
• do
•     {
•        cout << "value of a: " << a << endl;
•        a = a + 1;
•     }
•   while( a < 20 );
• return 0;
• }
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Exercise
• Write a program that asks the user
• Do you want to use this program? (y/n)
• If the user says ‘y’ then the program terminates
• If the user says ‘n’ then the program asks
• Are you really sure you do not want to use this
program? (y/n)
• If the user says ‘n’ it terminates, otherwise it prints
again the message
• Are you really really sure you do not want to use this
program? (y/n)
• And so on, every time adding one more “really”.
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C++ Basics

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