goto Statement

goto STATEMENT

The goto statement is used to transfer control to a specified label. However, the label must reside in the same function and can appear only before one statement in the same function. The syntax of goto statement is shown in Figure 3.11.

Here, label is an identifier that specifies the place where the branch is to be made. Label can be any valid variable name that is followed by a colon (:). The label is placed immediately before the statement where the control has to be transferred.

The label can be placed anywhere in the program either before or after the goto statement. Whenever the goto statement is encountered the control is immediately transferred to the statements following the label. Therefore, goto statement breaks the normal sequential execution of the program. If the label is placed after the goto statement, then it is called a forward jump and in case it is located before the goto statement, it is said to be a backward jump.

The goto statement is often combined with the if statement to cause a conditional transfer of control.

IF condition THEN goto label

In this book, we will not use the goto statement because computer scientists usually avoid this statement in favour of the 'structured programming' paradigm. Some scientists think that the goto statement should be abolished from higher-level languages because they complicate the task of analysing and verifying the correctness of programs (particularly those involving loops).

Programming Tip: Follow proper indentation for better clarity, readability, and understanding of the loops.

Moreover, structured program theory proves that the availability of the goto statement is not necessary to write programs, as combination of sequence, selection, and repetition constructs is sufficient to perform any computation. The code given below demonstrates the use of a goto statement. The program calculates the sum of all positive numbers entered by the user.

#include <stdio.h>

int main()

{

int num, sum=0;

read: // label for goto statement

printf("\n Enter the number. Enter 999 to end: ");

scanf("%d", &num);

if (num != 999)

{

if (num < 0)

goto read; // jump to label- read

sum += num;

goto read; // jump to label- read

}

printf("\n Sum of the numbers entered by the user is = %d", sum);

return 0;

}

Conclusion

• It is not necessary to use goto statement as it can always be eliminated by rearranging the code.

• Using the goto statement violates the rules of structured programming.

• It is a good programming style to use break, continue, and return statements in preference to goto whenever possible.

• Goto statements make the program code complicated and renders the program unreadable.

Note

One must avoid the use of break, continue, and goto statements as much as possible as they are techniques used in unstructured programming.

In structured programming, you must prefer to use if and if-else constructs to avoid such statements. For example, look at the following code which calculates the sum of numbers entered by the user. The first version uses the break statement. The second version replaces break by if-else construct.

// Uses break statement

#include <stdio.h>

int main()

{

int num, sum=0;

while (1)

{

printf("\n Enter any number. Enter 999 to stop: ");

scanf("%d", &num);

if (num==999)

break; // quit the loop

sum+=num;

}

printf("\n SUM = %d", sum);

return 0;

}

// Same program without using break statement

#include <stdio.h>

int main()

{

int num, sum=0, flag=1; // flag will be used to exit from the loop

while (flag = =1) // loop control variable

{

printf("\n Enter any number. Enter 999 to stop: ");

scanf("%d", &num);

if (num! 999)

sum+=num;

else

flag=0; // to quit the loop

{

printf("\n SUM= %d", sum);

return 0;

}

Now let us see how we can eliminate continue statement from our programs. Let us first write a program that calculates the average of all non-zero numbers entered by the user using the continue statement. The second program will do the same job but without using continue.

#include <stdio.h>

int main()

{

int num, sum=0, flag=1, count=0;

float avg;

// flag will be used to exit from the loop

while (flag==1)

{

printf("\n Enter any number. Enter 999 to stop: ");

scanf("%d", &num);

if (num==0)

continue; // skip the following statements

if (num!=999)

{

sum+=num;

count++;

}

else

flag=0;

// set loop cntl var to jump out of loop

}

printf("\n SUM %d", sum);

avg = (float) sum/count;

printf("\n Average %f", avg);

return 0;

}

// Same program without using continue statement

#include <stdio.h>

int main()

{

int num, sum=0, flag=1, count=0;

float avg; // flag will be used to exit from the loop

while (flag = =1)

{

printf("\n Enter any number. Enter 999 to stop: ");

scanf("%d", &num);

if (num!=0)

{

if (num!=999)

{

sum+=num;

count++;

}

else

flag=0;

}

}

printf("\n SUM= %d", sum);

avg = (float) sum/count;

printf("\n Average=%f", avg);

return 0;

}