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I've been programming a little calculator project in C++ just to train my skills (and hopefully give me a sense of achievement), but I'm encountering a problem with my while loop.

Essentially the program prompts the user for the 'mode'/command to use (e.g multiplication, division etc), and then calling the appropriate command. Once they've finished it should bring them back to the start (the while loop which is while true essentially) and start over again (return 0), with the option to quit (return 1). However, it quits instantly after the first time, even though. Am I doing something wrong? Do I seriously misunderstand C++ programming? Or what? Here is my code: (most functions cut out)

#include <iostream>


using namespace std;

int cMode(); // function prototypes
int add();
int sub();
int mult();
int divide();
int sqr();

int main() { // main function start
    do {
          cMode();
    } while (0);

    return 0;
}

int cMode() { // mode selection func
    int mode;
    cout<<"Please select which mode you would like to avail from the following:\n";
    cout<<"1. Addition\n2. Subtraction\n3. Multiplication\n4. Division\n5. Sqaure root finder\n6. Exit\n";
    cin>>mode;
    if ( mode == 1 ) {
        return add();
    }
}

int add() { // addition function
    int x, y; // variables

    cout<<"Please type the first number to add: ";
    cin>>x;
    cin.ignore();
    cout<<"Please type the second number to add: ";
    cin>>y;
    x = x + y;
    cout<<"The answer is "<< x <<".";
    return 0;
}

Anyway, if someone could help would be much appreciated. Also, two further little questions on the line with out<<"...."<< x <<;, why do I have to include the "" at the end for it to run? I was getting an error with them, and why cant I put endl at the end of the "" on a cout line?

Thanks!

Wajahat
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wolf_adventures1909
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    `} while (0);` should probably be `} while (1);` – DimChtz Aug 03 '16 at 19:37
  • @DimChtz no, it should probably be `while (variable)` where `variable` was set with the return value of the function. – Mark Ransom Aug 03 '16 at 19:38
  • You're meant to use the editor you prefer and then paste in your code. If they tried to set up keybinds everyone liked, no one would like it ;) – jaggedSpire Aug 03 '16 at 19:38
  • You're _not_ checking the return of `cMode` - you're just testing `0`. And in C/C++, `0` means _false_ (non-zero means true). Which is a good reason these are bad values to choose for signaling ... – davidbak Aug 03 '16 at 19:39
  • >> why cant I put endl at the end of the "" on a cout line? cout << "Hello world" << endl; works fine for me – alekscooper Aug 03 '16 at 19:40
  • @MarkRansom That's another story. Obviously OP wants an infinite loop or maybe he plans to use a `break` depending on what `cMode()` returns. I just pointed him why his loop stops. – DimChtz Aug 03 '16 at 19:40
  • @davidbak, what would be a good value for signaling? I though 0 was true, which is what the root of the issue is. – wolf_adventures1909 Aug 03 '16 at 20:06
  • @wolf_adventures1909 - when you get to that point in your studies: that's what enums (enumerated values) are for. As you've learned here, `0` is false. (You may be confused if you're from a Unix command line background where a `0` exit code is success - the opposite of here.) And that isn't the root of the issue: The root of the issue is you're _not_ testing the return value of the function `cNode` in that `while` expression. You're not even saving it to a variable so you could have it to test. – davidbak Aug 03 '16 at 20:16
  • @davidbak I fixed it by putting ret = cMode(); and then putting ret in the while loop, which works perfectly for now. – wolf_adventures1909 Aug 03 '16 at 20:32

2 Answers2

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Problem is here:

int main() { // main function start
    do {
       cMode();
    } while (0);
}

It will execute the do {} part and then since condition in while is 0 it exits. do-while executes until the condition evaluates to a non-zero value.

You probably want to create a variable and store the return value from cMode() and then have something like:

int main() { // main function start
    int ret=0;   
    do {
       ret=cMode();
    } while (ret);
}

By the way, for this to work, you need to make sure that cMode() returns 0 only if user selects mode 6 (Exit).

NVM Edited your question, as that was a code formatting issue: And another thing, maybe it is a question formatting problem but you have your add() function inside the main() and I don't think that works in c++.

Community
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Wajahat
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0

You should do:

#include <iostream>


using namespace std;

int cMode(); // function prototypes
int add();
int sub();
int mult();
int divide();
int sqr();

int main() { // main function start
    while (cMode() == 0); //This keep the loop
    return 0;
}

int cMode() { // mode selection func
    int mode;
    cout<<"Please select which mode you would like to avail from the following:\n";
    cout<<"1. Addition\n2. Subtraction\n3. Multiplication\n4. Division\n5. Sqaure root finder\n6. Exit\n";
    cin>>mode;
    if ( mode == 1 ) {
        return add(); //all functions should return 0 in success
    }
    if ( mode == 6) {
        return 1; //returning 1 exits the loop
    }
}

int add() { // addition function
    int x, y; // variables

    cout<<"Please type the first number to add: ";
    cin>>x;
    cin.ignore();
    cout<<"Please type the second number to add: ";
    cin>>y;
    x = x + y;
    cout<<"The answer is "<< x <<".";
    return 0;
}

The problem is that while(0) is the same as saying while(false) so it evaluates to false and end...

DIEGO CARRASCAL
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