if statement followed by return 0-CodePudding

I have some code like:

#include <iostream>
#include <string>

int main() {
    std::string question;

    std::getline(std::cin, question);
    
    if (question == "yes") {
        std::cout << "Let's rock and roll!" << std::endl;
        return 0; // This line
    } if (question == "no") {
        std::cout << "Too bad then..." << std::endl;   
    } else {
        std::cout << "What do you mean by that?" << std::endl;
    }
    return 0;
}

If I don't write the commented return 0 line and input yes, the output is Let's rock and roll! followed by What do you mean by that?. It should only output Let's rock and roll!.

But I don't need to put return 0 in the if (question=="no"){...} block. If I input no, the output is just Too bad then....

Why do I need the return 0 in the first case, but not the second?

CodePudding user response：

Control flow is your issue here:

     if(question == "yes"){
        std::cout<<"Lets rock and roll!"<<std::endl;
        return 0;
     }if (question == "no"){
        std::cout<<"Too bad then..."<<std::endl;   
     } else{
        std::cout<<"What do you mean by that?"<<std::endl;
     }

Let's format this a bit better.

     if (question == "yes") {
        std::cout << "Lets rock and roll!" << std::endl;
        return 0;
     }

     if (question == "no") {
        std::cout << "Too bad then..." << std::endl;   
     } 
     else {
        std::cout << "What do you mean by that?" << std::endl;
     }

These are two different conditionals. The first one being triggered does not stop the second if/else from being evaluated. In fact, if question equals "yes" then it cannot equal "no" so the else clause in the second if/else must be executed.

By including return 0; in the first conditional block, the function exits immediately, thus skipping everything after it. The second if/else is not evaluated and "What do you mean by that?" is never printed.

You likely wanted this to be a single if/else. Now only one of these blocks will be executed.

     if (question == "yes") {
        std::cout << "Lets rock and roll!" << std::endl;
     }
     else if (question == "no") {
        std::cout << "Too bad then..." << std::endl;   
     } 
     else {
        std::cout << "What do you mean by that?" << std::endl;
     }