goto STATEMENT IN C/C++

What is goto statement in C/C++?

The goto statement is a jump statement in C/C++ which is also called unconditional jump statement. It is used to transfer control from any point in a function to some other point (called label).

Let us look into the working of goto statement. Here we define a label (which is a user-defined identifier). We then write a statement or a block of statements under that label. So now whenever we refer to that label, we are actually referring to those statements. Whenever the compiler reads the statement goto label, it passes the control to that label and starts executing from there. Note here that a label name can be any valid identifier.

Here are 2 basic syntax for goto statement :

Type 1 :    label : statement;

                  …//may be some code

                  goto label;

Type 2 :    goto label;

                   …//may be some code

                   label : statement;

 

What is the scope of goto statement?

A goto statement is valid only if it passes control to a label in the same function. Referencing a label outside the function in which it is defined gives compilation error. But within a function a goto statement and a label can be placed anywhere (i.e. maybe type 1 or type 2 ).

See the following code :

void Sum()

 {

    label : cout<< “Sum”;

 }

int main()

 {

    goto label;

    return 0;

 }

This code gives the following error message:

[error] label ‘label’ used but not defined

 

Let us see a demo code and understand its working using a flowchart.

//demo run for goto statement

label1 : statement1;

goto label3;

label2 : statement2;

label3 : statement3;

 

 A demo program in C++ :

//find and print all odd numbers

//from 1 to 10 using goto

#include<iostream>

using namespace std;

int main()

{

    int n= 1;

    label :

         if(n%2 != 0)

            cout<<n<< “ ”;

    n++;

    if(n<=10)

         goto label;

    return 0;

}

Output : 1 3 5 7 9

 

Executing both if & else statement simultaneously

We know, in using if-else construct, either the if or the else statement is executed but never both. This is required for correct decision making process. However, the statement that if and else statements cannot be executed simultaneously is not true.

As we have learnt earlier in this article, goto statement can be used to transfer control from any point to the other in a function. So, can we use it to jump from if part to else part? The answer is yes! Let us see an example :

//code to jump from if to else

if(condition)

   {

      statement1;

      goto label2;

   }

else

   label2 : statement2;

Now if the condition is true, the control will enter if and execute statement1. Then it will jump to label2 and execute statement2.

However always be careful when using goto because you may easily end up having an infinite loop.

 

Why goto statement is not used by programmers?

You must have noticed that although the concept of goto sounds so important, it is not generally used in programs. There are a few reasons for it :

First, using goto in a program makes the logic very complex. You need to take extra care about the control positions and be sure the control doesn’t get trapped in an infinite loop.

Second, reading a program developed by some other programmer who has used goto can be really tough. It becomes very hard to debug and correct the program.

Third, better and safer options of jump control are available in C/C++ as break and continue statements. These statements give the desired result without causing much trouble.

 

 

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