goto Statement in C

Syntax for goto Statement

1. Defining the Label

Syntax: label_name: (insert code block)

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The label_name acts as an identifier and names a specific code block. 

When a goto statement is iterated upon, the execution control approaches the label_name of a particular block, and that code block will be executed. 

Just like variables, each label name has to be distinctive.

2. Transferring the Execution Control

Syntax: goto label_name; (insert code block)

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With this command, the user can jump the execution control to the specific line in the code where the label_name is used.

The label can be positioned anywhere in the code above or below the goto statement.

Examples of goto Statement

Example 1- Printing numbers in a given range 

Lets see a program to print the numbers between two input numbers using goto statement.

int main()
{
    int start, end, curr;
    printf("Enter two numbers: ");
    scanf("%d %d",&start, &end);

    curr = start;
    
    // defining label
    
    print_line :
            printf("%d ", curr);
        if(curr<end)
        {
            curr++;
            // using goto statement
            
            goto print_line;
        }
    return 0;
}

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Output

Enter two numbers: 3 18
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 

Explanation

In the above program, after initialising integer variables, the user is asked to input two numbers for the calculation of factorial. The variable ‘curr’ is set to the same value as the variable ‘start’. Then, a label called ‘print_line’ is defined.

If the value of ‘curr’ is greater than or equal to the value of ‘end’, the code enters the loop; and if the value is less than ‘end’, the value of ‘curr’ increments by 1 and the goto statement jumps back to the label.

Example 2- Calculating the factorial of a number

Let’s see a program for calculating the factorial of a number using a goto statement.

 #include<stdio.h>
 int main()
 {
   int num;
   long fact = 1;
   printf("Enter any number: ");
   scanf("%d",&num);
   
   if(num<0) goto end;
   for(int i=1; i<=num; i++)
   fact = fact * i;
   printf("Factorial of %d is = %ld", num, fact);
   end:
   
   return 0;
 }

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Output

Enter any number: 4
Factorial of 4 is = 24

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Explanation

In the above program, In the above code we used for loop and goto statement for calculating the factorial of the number 4.

Here, i = 1 and is incremented in every iteration till it reaches ‘num’. ‘Fact’ is multiplied by ‘i’ and then stored in ‘fact’, during each iteration.

Note: In cases where the input is large, there may be possibilities of integer overflow. This is due to the limitations of ‘int’. This overflow results in false or negative results. To overcome this problem, one should use a larger data type.

 Let us take another example of the output.

Output

Enter any number: 22
Factorial of 22 is = -1250660718674968576

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The output in the above test case is in negative due to the integer overflow.

Styles of Implementing goto Statement in C

There exist two styles of goto Statements:

Style 1: Transferring the Control from Down to the Top

	label-name:
    statement1;
    statement2;
    ..
    if(test-condition)
        goto label-name;

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Style 2: Transferring the Control from Top to Down

statements;
    if(test-condition)
        goto label-name;
    statement1;
    statement2;
    label-name:
        Other statements;

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How Does the goto Statement Work in C?

The `goto` statement in C allows jumping to labeled statements, disrupting the normal flow. It's discouraged due to complex, unreadable code. Favor structured constructs like loops and conditionals for better code organization and maintainability.

Also see, Floyd's Triangle in C

Program to Understand the goto Statement in C

In this example, we will implement a goto statement where the program to calculate the sum and average of positive numbers will be created, and if the user enters a negative number, then the goto statement will be executed, and the sum and average are displayed.

#include <stdio.h>
int main() {
  int maxInput = 6, i;
  double number, average, sum = 0.0;
  
  for(i = 1; i <= maxInput; ++i) {
     printf("%d. Enter a number: ", i);
     scanf("%lf", &number);
     
   //  goto statement is added if the value is -ve number.
     if (number < 0.0)
        goto jump;
        
     sum += number;
  }
jump:
  average = sum / (i - 1);
  printf("Sum: %.2f\n", sum);
  printf("Average: %.2f", average);
  return 0;
}

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Output

When to use the goto Statement?

The use of the goto statement is preferable when there is a need to break multiple loops using one single statement at the same time. It can also be used to transfer to any place within the program where the goto statement is called upon.

Should One Use goto?

If using a goto statement makes your code easier and simplifies your problem, then you're good to go ninja! 

But there exists a considerable amount of debate about goto statements. Since goto statements make it harder to trace the control flow of a program, they often need to be fully understood by the programmers and are not that easy to modify. The use of goto makes the program buggy as well. Furthermore, the goto statement is hardly put to use. 

Advantages of goto Statement in C

• By using the goto statement, jump to a part above the current flow as well as any other part of the current flow.
   
• Using a goto statement removes the need to use for and while loops in the program.
   
• The runtime speed of the code efficiently increases when the goto statement is put in place to skip a particular part of the code after one condition is satisfied.
   
• Using one got statement allows you to break out of all loops, unlike the multiple break statement.

Disadvantages of goto Statement in C

goto Statement makes the program hard to read and follow.

• Further, it adds to the complexity of the code.
   
• It makes the code buggy.
   
• Multiple goto statements alter the program's flow and confuse the readers. 

Frequently Asked Questions

What is the problem with the goto statement in C?

The goto statement is used to jump to and from places within a function. When there is a need to jump from one statement to another, jump from one block to another.

What is the purpose of the goto statement in C?

The purpose of the goto statement is that there is a need to break multiple loops using one single statement at the same time. It can also be used to transfer to any place within the program where the goto statement is called upon.

Can goto be used between functions?

Yes, a goto statement can be used between the functions in C, which can be used while skipping a few lines in the program, where a goto statement is used.

Why is goto not used in C

The goto statement is avoided in C because it can make code harder to read, understand, and maintain, leading to "spaghetti code."

How to avoid goto in C?

Avoid goto in C by using structured programming constructs like loops, conditionals, and functions to manage control flow and enhance code clarity.

Is goto a valid jump statement?

Yes, goto is a valid jump statement in C++. It transfers control to a labeled statement within the same function. However, it is rarely used as it can make code harder to read and maintain.

Conclusion

This article covered all the possible elements of goto Statements in c. We hope this article has helped you in your journey of learning. Here are some recommendations for you to visit our articles on different topics of C, such as

• Getch in C
• Jump Statements
• Flow Control
• Conditional Operator in C
• Basic Blocks and Flow Graphs in Compiler Design
• Jump Statements in Java
• Ternary Operator in C
• Bubble Sort Program in C