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CMSC 104, Version 8/06 L15Switch.ppt
Power Point Presentation
In
Loop Case Statement
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The Source of Looping Statement
in
Programming
• #include <iostream>
•
• int main()
• {
• using namespace std;
•
• // nSelection must be declared outside do/while loop
• int nSelection;
•
• do
• {
• cout << "Please make a selection: " << endl;
• cout << "1) Addition" << endl;
• cout << "2) Subtraction" << endl;
• cout << "3) Multiplication" << endl;
• cout << "4) Division" << endl;
• cin >> nSelection;
• } while (nSelection != 1 && nSelection != 2 &&
• nSelection != 3 && nSelection != 4);
•
• // do something with nSelection here
• // such as a switch statement
•
• return 0;
• }
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The Screen Shot on Looping Statement
in
Programming

The Explanation of Looping Statement
in
Programming
• The statement in a do while loop always executes at least once. After the
statement has been executed, the do while loop checks the condition. If the
condition is true, the CPU jumps back to the top of the do while loop and
executes it again.
• Here is an example of using a do while loop to display a menu to the user and
wait for the user to make a valid choice:
• One interesting thing about the above example is that the nSelection variable
must be declared outside of the do block. Think about it for a moment and see
if you can figure out why that is.
• If the nSelection variable is declared inside the do block, it will be destroyed
when the do block terminates, which happens before the while conditional is
executed. But we need the variable to use in the while conditional —
consequently, the nSelection variable must be declared outside the do block.
• Generally it is good form to use a do while loop instead of a while loop when
you intentionally want the loop to execute at least once, as it makes this
assumption explicit — however, it’s not that big of a deal either way.

in
Programming
#include <iostream>
using namespace std;
enum Logical {False, True};
Logical acceptable(int age, int score);
/* START OF MAIN PROGRAM */
int main()
{
int candidate_age, candidate_score;
cout << "Enter the candidate's age: ";
cin >> candidate_age; cout << "Enter the candidate's
score: ";
cin >> candidate_score;
if (acceptable(candidate_age, candidate_score))
cout << "This candidate passed the test.n";
else
cout << "This candidate failed the test.n";
return 0;
}

in
Programming
Indeed, we can now use the identifier "Logical" in exactly the same way as we use the
identifiers "int", "char", etc. In particular, we can write functions which return a value of type
"Logical". The Following example program takes a candidate's age and test score, and
reports whether the candidate has passed the test. It uses the following criteria: candidates
between 0 and 14 years old have a pass mark of 50%, 15 and 16 year olds have a pass
mark of 55%, over 16's have a pass mark of 60%:
Defining our own data types (even if for the moment they're just sub-types of "int") brings us
another step closer to object-oriented programming, in which complex types of data structure
(or classes ofobjects) can be defined, each with their associated libraries of operations.

in
Programming
• void main ()
• {
• int x;
• do
• {
• cout << "Input the number:";
• cin >> x;
• cout << "The number is:" << x << "n";
• } while (x != 5);
• cout << "End of program";
• }

CMSC 104, Version 8/06 1L15Switch.ppt
in
Programming
In this example, the input number is 5 and the while
loop is executed starting from 5 until the number
reaches a value <0.Whilethe value of x>0 the
statement inside the while block prints the value of x.
When this is completed, the numbers 5, 4, 3, 2, 1
are
printed. After the value of x reaches less than zero,
the control passes to outside the while block and
EXFORSYS is printed.

in
Programming
• void main ()
• {
• int x;
• do
• {
• cout << "Input the number:";
• cin >> x;
• cout << "The number is:" << x << "n";
• } while (x != 5);
• cout << "End of program";
• }

in
Programming

in
Programming
The do while loop functionality is similar to
while loop. The main difference in do-while
loop is that the condition is checked after the
statement is executed. In do-while loop, even
if the condition is not satisfied the statement
block is executed once.

in
Programming
• /* END OF MAIN PROGRAM */ /*
• FUNCTION TO EVALUATE IF TEST SCORE IS ACCEPTABLE */
• Logical acceptable(int age, int score)
• {
• if (age <= 14 && score >= 50)
• return True;
• else if (age <= 16 && score >= 55)
• return True;
• else if (score >= 60)
• return True;
• else return False;
• }
• /*END OF FUNCTION */

in
Programming
There is a third kind of "loop" statement in C++
called a "do ... while" loop. This differs from "for" and
"while" loops in that the statement(s) inside
the {} braces are always executed once, before the
repetition condition is even checked. "Do ... while“
loops are useful, for example, to ensure that the
program user's keyboard input is of the correct
format:

Power Point Presentation
In
Switch Case Statement

The Source Code of Switch Case Statement
in
Programming
#include <iostream>
int main ()
{
char permit;
cout << "Are you sure you want to quit? (y/n) : ";
cin >> permit;
switch (permit)
{
case 'y' :
cout << "Hope to see you again!" << endl;
break;
case 'n' :
cout << "Welcome back!" < < endl;
break;
default:
cout << "What? I don't get it!" << endl;
}
return 0;
}

The Screen Shot of Switch Case Statement
in
Programming

The Explanation of Switch Case Statement
in
Programming
The program that we create should be readable. To increase
the readability of the program we should use tools that is
simple to read and understand. When possible use switch
statement rather than if else statement, as it can be more
readable than if else statement. But switch statement has
limitation. It can't replace if else completely but can be helpful
at certain situation. It can't do everything thing that if else
statement can do. For example, switch statement can take
only int or char datatype in c++. The following programs will
help you to understand the switch statement.

in
Programming
#include <iostream>
#include <iomanip>
int main ()
{
const int CHEESE_PIZZA = 11;
const int SPINACH_PIZZA = 13;
const int CHICKEN_PIZZA = 14;
cout << " *********** MENU ***********" << endl;
cout << setw (9) << "ITEM" << setw (20) << "PRICE" << endl;
cout << " (1) Cheese Pizza" << setw (8) << "$"
<< CHEESE_PIZZA << endl;
cout << " (2) Spinach Pizza" << setw (7) << "$"
<< SPINACH_PIZZA << endl;
cout << " (3) Chicken Pizza" << setw (7) << "$"
<< CHICKEN_PIZZA << endl;
cout << endl;
cout << "What do you want? ";
int option;
cin >> option;
cout << "How many? ";
int quantity;
cin >> quantity;
int price;
switch (option)
{
case 1:
price = CHEESE_PIZZA;
break;
case 2:
price = SPINACH_PIZZA;
break;
case 3:
price = CHICKEN_PIZZA;
break;
default:
cout << "Please select valid item from menu. " <<
endl;
return 1;
}
int amount = price * quantity;
cout << "Your Bill: $ " << amount << endl;
return 0;
}

in
Programming

in
Programming
In the above program we take an integer value from the user which is
stored in 'option' variable. We pass this value to switch statement. The
switch statement has 3 cases: case 1, case 2 and case 3. The case 1: is
similar to if (option == 1). This is the advantage of switch statement over if
else statement. You don't need to type the name of variable again and
again if you are doing selection operation on same variable. You just put
the variable name on switch statement and then just specify the value
after 'case'. One more thing to be noted is that it requires 'break‘
statement at the end of each 'case'. If you remove the break statement
then it will jump to the case that follows it. Try it and check by yourself.
The 'default' is same as else in if else statement.

in
Programming
#include <iostream>
void playgame()
{
cout << "Play game called";
}
void loadgame()
{
cout << "Load game called";
}
void playmultiplayer()
{
cout << "Play multiplayer game called";
}
int main()
{ int input;
cout<<"1. Play gamen";
cout<<"2. Load gamen";
cout<<"3. Play multiplayern";
cout<<"4. Exitn";
cout<<"Selection: ";
cin>> input;
switch ( input )
{
case 1: // Note the colon, not a
semicolon
playgame(); break;
semicolon
loadgame(); break;
semicolon
playmultiplayer(); break;
semicolon cout<<"Thank you for playing!n";
break;
default: // Note the colon, not a semicolon
cout<<"Error, bad input, quittingn"; break;
}
cin.get();
}

in
Programming

in
Programming
This program will compile, but cannot be run until the
undefined functions are given bodies, but it serves as a
model (albeit simple) for processing input. If you do not
understand this then try mentally putting in if statements for
the case statements. Default simply skips out of the switch
case construction and allows the program to terminate
naturally. If you do not like that, then you can make a loop
around the whole thing to have it wait for valid input. You
could easily make a few small functions if you wish to test
the code.

in
Programming
// custom countdown using while
#include <iostream>
int main ()
{
int n;
cout << "Enter the starting number > ";
cin >> n;
while (n>0) {
cout << n << ", ";
--n;
}
cout << "FIRE!n";
return 0;
}

in
Programming
• When the program starts the user is prompted to insert a starting number for the countdown. Then the while loop begins, if the
value entered by the user fulfills the condition n>0 (that n is greater than zero) the block that follows the condition will be
executed and repeated while the condition (n>0) remains being true.
The whole process of the previous program can be interpreted according to the following script (beginning in main):
User assigns a value to n
• The while condition is checked (n>0). At this point there are two possibilities:
* condition is true: statement is executed (to step 3)
* condition is false: ignore statement and continue after it (to step 5)
• Execute statement:
cout << n << ", ";
--n;
(prints the value of n on the screen and decreases n by 1)
• End of block. Return automatically to step 2
• Continue the program right after the block: print FIRE! and end program.
•
When creating a while-loop, we must always consider that it has to end at some point, therefore we must provide within the block
some method to force the condition to become false at some point, otherwise the loop will continue looping forever. In this case
we have included --n; that decreases the value of the variable that is being evaluated in the condition (n) by one - this will
eventually make the condition (n>0) to become false after a certain number of loop iterations: to be more specific,
when n becomes 0, that is where our while-loop and our countdown end.
Of course this is such a simple action for our computer that the whole countdown is performed instantly without any practical
delay between numbers.

in
Programming
#include <stdlib.h>
#include <stdio.h>
int main(void) {
int n;
printf("Please enter a number: ");
scanf("%d", &n);
switch (n) {
case 1: {
printf("n is equal to 1!n");
break;
}
case 2: {
break;
}
case 3: {
break;
} default: {
printf("n isn't equal to 1, 2, or 3.n");
break;
}
}
system("PAUSE");
return 0;
}

in
Programming

in
Programming
The switch statement is used in C++ for testing if a
variable is equal to one of a set of values. The variable
must be an integer, i.e. integral or non-fractional. The
programmer can specify the actions taken for each
case of the possible values the variable can have. The
same operation can be performed by using a series of
if, else if, and else statements as was demonstrated
in Lesson 03: Else If Statements. Therefore, let's look
at an example using the switch statement that mimics
the functionality of the Else If Example from Lesson
03.

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