return 0 vs return 1 in C++

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 to article return statement in C/C++ with examples.

There are two scenarios in which return statements will be 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 will be 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.
• The 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.

Time Complexity: O(1)
Auxiliary Space: O(1)

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

Time Complexity: O(1)
Auxiliary Space: O(1)

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.