C Programming Tutorial – Flow Control – II

In the previous lesson, we learned about the flow control structure. We learned about the if-else structures and nested if structures. In this lesson, we will learn about another flow control feature – switch-case.

If-else Construct

Consider a C program for calculator, the user is given a menu with options to choose from.

  1. Add
  2. Subtract
  3. Multiply
  4. Divide

We can write a program using if-else construct for the above problem.


#include <stdio.h>

int main()
{

    int choice;

    int a,b,c;

    a = 10;

    b = 20;

    printf (“Enter your choice:”);

    if (choice == 1)

    c = a+b;

    if (choice == 2)

    c = a – b;

    if (choice == 3)

    c = a * b;

    else if(choice == 4)

    c = a/b;

    else
    {

    printf(“Wrong input, Try again!”);

    }

    getch();

    return 0;

}

The user enters a number and it is matched with if-else blocks and whenever there is a match that block is executed.

The problem with these kinds of the construct is that when the menu is large, then the if-else construct will be difficult to manage. Also, there are many comparisons – each if a block is tested.

Switch-Case

The switch-case is suitable for menu driven C programs. Whenever the program is executed, a menu with a number of choices like the example below is presented to the user.

/* Calculator Application in C */

Enter your choice:

  1. Add
  2. Subtract
  3. Multiply
  4. Divide

The switch block look like the following in program source code. The switch block accepts a number as user choice.

When the user enters a number next to an option and the Switch accepts the choice(number).

int choice;

Switch (choice)
{

}

The switch () matches the user choice with a list of cases. Each of the cases has a number associated with them followed by a colon.

Case 2:

    Statement1;

    break;

Case 3:

    Statement2;

    Statement3;

    break;

When the user choice and the case number matches, the statements from the case is executed and terminated by a break; statement.

The entire switch-case block look like following

int choice;

scanf(“%d”,&choice);

Switch(choice)
{

Case 1:

    Do something;

    break;

Case 2:

    Do something;

    break;

default:

    Do something;

    break;

}

Let’s create an example program using the Switch-Case. We shall write the Calculator program using the Switch-Case.

Flowchart – C Calculator

Flowchart - Switch-Case

Flowchart – Switch-Case

Program Code

/* C Program for a Calculator using Switch-Case */

#include 

int main()
{

    int choice;

    int a, b, c;

    a = 10;

    b = 20;

    printf (“Enter your choice:”);
 
    scanf (“%d”, &choice);

    Switch (choice)
    {

    case 1:

        c = a + b;

        break;

    case 2:

        c = a - b;

        break;

    case 3:

        c = a * b;

        break;

    case 4:

        c = a / b;

        break;

    default:

        printf (“Wrong choice, try again!”);

        break;

    }

    printf (“Result = %d\n”, c);

    getch();

    return 0;

}

Output

The output of the program is given below.

Output-Switch-case

Output-Switch-case

Bibliography

Balagurusamy, E. 2000. Programming in ANSI C. Tata McGraw-Hill Education,.

Kanetkar, Yashavant. 20 November 2002. Let us C. Bpb Publications.