return 0 vs return 1 in C++

Difficulty Level : Basic
Last Updated : 06 Jan, 2021

The Return statement in C/C++:

C and C++ support return statements which are also called jump statements.
It is used to return a value from the function or stop the execution of the function. For more information on return statements please refer article return statement in C/C++ with Examples.

There are two scenarios in which return statements are used:

Method 1. Inside the main function:

In this case, the return statement stops the execution of the program, and 0 or 1 will denote the execution status.
These status codes are just used as a convention for a long time in C language because the language does not support the objects and classes, and exceptions.
return 0: A return 0 means that the program will execute successfully and did what it was intended to do.
return 1: A return 1 means that there is some error while executing the program and it is not performing what it was intended to do.

Important characteristics of the return statement:

If exit with a status other than 0 then, print an error message to stderr.
There are different conventions depending on the operating system about return codes.
Operating System may itself terminate the program with specific exit status codes if some invalid operations are performed.

Below is a program to illustrate the use of return 0 and return 1 inside the main function:

C++

// C++ program to divide two numbers
#include <iostream>
using namespace std;
  
// Driver Code
int main()
{
    // Given integers
    int a = 5, b = 0;
  
    if (b == 0) {
  
        // The below line is used to print
        // the message in the error window
        // fprintf(stderr, "Division by zero"
        //                 " is not possible.");
  
        // Print the error message
        // as return is -1
        printf("Division by zero is"
               " not possible.");
        return -1;
    }
  
    // Else print the division of
    // two numbers
    cout << a / b << endl;
  
    return 0;
}

Output:

Division by zero is not possible.

Method 2. Inside the user-defined function:

C++ treats boolean as a completely separate data type that has only 2 distinct values i.e., true and false.
The values 1 and 0 are of type int and are not implicitly convertible to boolean that means:
- return 0: returning false from a function.
- return 1: returning true from a function.

Below is a program to illustrate the use of return 0 and return 1 inside the user-defined function:

C++

// C++ program to demonstrate the use
// of return 0 and return 1 inside
// user-defined function
#include <iostream>
using namespace std;
  
// Utility function returning 1 or
// 0 based on given age
int checkAdultUtil(int age)
{
    if (age >= 18)
        return 1;
    else
        return 0;
}
  
// Function to check for age
void checkAdult(int age)
{
    // Checking on the basis
    // of given age
    if (checkAdultUtil(age))
        cout << "You are an adult\n";
    else
        cout << "You are not an adult\n";
}
  
// Driver Code
int main()
{
    // Given age
    int age = 25;
  
    // Function Call
    checkAdult(age);
  
    return 0;
}

Output:

You are an adult

Conclusion:

Use-case	return 0	return 1
In the main function	return 0 in the main function means that the program executed successfully.	return 1 in the main function means that the program does not execute successfully and there is some error.
In user-defined function	return 0 means that the user-defined function is returning false.	return 1 means that the user-defined function is returning true.

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