SWITCH CASE AND GOTO STATEMENT IN C

Switch case:

We studied earlier in decision control that how and when to use if, if-else.

They are good enough to select one from the two available options. When choices are two, we can use if-else. Even if we have multiple choices we can use multiple if-else, sometimes we use if-else ladder or nested if-else.  You probably experienced that as the number of available options/choices are large, if-else becomes complex.

So when we have many choices, we can use switch case control in place of if-else.

In this section we are going to use three key switch, case and default.

Syntax of switch case

main()

{

            ….

            ….

            switch( expression)

            {

                        case constant1 :

                                                ….

                        case constant2 :

                                                ….

                        case constant3 :

                                                ….

                        …

                        default:

                                    ……

            }

            …..

}

Switch case control is used when user have multiple choices. Switch transfers the control to a case written in its body depending on the value evaluated by expression in switch parenthesis. In switch body each case is post fixed by a constant. This constant could be integer or character but not real. It is also worth mentioning here that the constant in each case must be distinct.

When value of expression does not match with any case constant then control moves on default segment.

Another important point to notice that once control moves from switch to appropriate case, it not just execute statement written in that case but also execute all the statements written in following cases including default, but not cases written above. If you are concern with only one case execution, use break keyword as the last statement of every case.

Switch case control is very useful in menu driven program. The following example illustrates menu driven program. It is also use break to terminate switch.

main()

{

            int a, b, result, ch;

           

            while(1) // condition is always true, thus an infinite loop

            {

                        clrscr();

                        printf(“\n1. Addition”);

                        printf(“\n2. Subtraction”);

                        printf(“\n3. Multiplication”);

                        printf(“\n4. Division”);

                        printf(“\n5. Exit”);

                        printf(“\n\nEnter your choice”);

                        scanf(“%d”,&ch);

                        switch(ch)

{

            case 1:

                        printf(“Enter two numbers”);

                        scanf(“%d%d”,&a,&b);

                        result=a+b;

                        printf(“Sum is %d”, result);

                        break; //it is used to move control out of switch body

            case 2:

                        printf(“Enter two numbers”);

                        scanf(“%d%d”,&a,&b);

                        result=a-b;

                        printf(“Difference is %d”, result);

                        break; //it is used to move control out of switch body

            case 3:

                        printf(“Enter two numbers”);

                        scanf(“%d%d”,&a,&b);

                        result=a*b;

                        printf(“Product is %d”, result);

                        break; //it is used to move control out of switch body

            case 4:

                        printf(“Enter two numbers”);

                        scanf(“%d%d”,&a,&b);

                        result=a/b;

                        printf(“Quotient is %d”, result);

                        break; //it is used to move control out of switch body

            case 5:

                        exit(0);

            default:

                        printf(“Invalid Entry”);

}

getch();

            }

}

Explanation:

There are few things to discuss about above program.

1)      Notice while loop which executes infinite times till you select 5 from the menu.

2)      In case 5, we use a predefined function exit. The job of this function is to terminate program.

3)      The keyword break is used in each case as it transfers the control outside switch body.

4)      Whenever wrong selection from menu (other than value from 1 to 5) switch moves the control to default segment.

5)      No need to put keyword break after default statements as it is already at the end of switch body.

6)      Rest you can understand the flow of program by executing it.

goto control

The goto statement is used for unconditional jump from one part of the program to another part of the program. It is always suggested not to use goto statement as this reduces the readability of the program. Using goto statement is considered as poor programming approach

Example

main()

{

.           int cm;

            printf(“Enter length in centimeters”);

            scanf(“%d”,&cm);

            if(cm<100)

                        goto label;

            cm=cm%100;

            printf(Wrong input is trimed”);

           

     label:

            printf(“cm=%d”, cm);

}

           

Explanation:

1)      goto is a keyword that moves control to a location in the program mentioned by location name ‘label’.

2)      If value of cm is more than or equal to 100, it should be trimmed. For example if user enters 435, it becomes 35, 4 should be trimmed out.

3)      Try executing this program for different inputs.

More points about goto

1)      goto can move control in forward as well as backward in the program.

2)      goto works only with in the same function body.

3)      Labels are names but no need to declare them as variables.