new question: understanding parse error

This is a discussion on new question: understanding parse error within the C++ Programming forums, part of the General Programming Boards category; I normally program in PHP, but I'm starting to learn C++ as well. Most of this is making sense, but ...

  1. #1
    Pig
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    new question: understanding parse error

    I normally program in PHP, but I'm starting to learn C++ as well. Most of this is making sense, but I am getting a parse error when compiling that doesn't make sense to me. My goal is to create a simple program that:
    1. displays a menu, and ask for a choice
    2. displays text based on the answer, and then goes back to #1.

    I compared my code against the tuts I'm reading, and everything looks fine (though it obviously isn't).

    Here is the compiler log:
    Compiler: Default compiler
    Executing g++.exe...
    g++.exe "C:\[c++]\pig.cpp" -o "C:\[c++]\pig.exe" -g3 -I"C:\Dev-Cpp\include\c++" -I"C:\Dev-Cpp\include\c++\mingw32" -I"C:\Dev-Cpp\include\c++\backward" -I"C:\Dev-Cpp\include" -L"C:\Dev-Cpp\lib"
    C:/[c++]/pig.cpp: In function `int main()':
    C:/[c++]/pig.cpp:9: parse error before `{' token
    C:/[c++]/pig.cpp:17: `display_answer' undeclared (first use this function)
    C:/[c++]/pig.cpp:17: (Each undeclared identifier is reported only once for each
    function it appears in.)
    C:/[c++]/pig.cpp: In function `int display_answer(int)':
    C:/[c++]/pig.cpp:20: `int display_answer(int)' used prior to declaration
    C:/[c++]/pig.cpp:25: `display_menu' undeclared (first use this function)
    C:/[c++]/pig.cpp: At global scope:
    C:/[c++]/pig.cpp:37: ISO C++ forbids declaration of `display_menu' with no type
    C:/[c++]/pig.cpp:37: `int display_menu()' used prior to declaration
    C:/[c++]/pig.cpp:38: parse error before `return'
    Execution terminated

    Here is the code:
    Code:
    #include <iostream>
    using namespace std;
    int display_answer(int choice);
    
    int main()
    {
        cout << "Let's just get this damn thing to compile before calling the function.\n";
        int display_menu()
        {
            cout << "What do you want to know?\n";
            cout << "(choose a number)\n\n";
            cout << "\t[1] Boxers or briefs?\n";
            cout << "\t[2] How pretty are you?\n";
            cout << "\t[3] Can I touch you?\n";
            int choice;
            cin>>choice;
            display_answer(choice);
        }
        int display_answer(int choice)
        {
            switch(choice)
            {
                case 1:
                    cout << "Boxer-breifs.\n";
                    display_menu();
                    break;
                case 2:
                    cout << "7.2\n";
                    display_menu();
                    break;
                case 3:
                    cout << "No.\n";
                    display_menu();
                    break;
            }
        }
        display_menu();
        return 0;
    }
    I figured start at the top, which is the parse error for
    int display_menu()
    {

    Can someone please enlighten me? TIA

  2. #2
    Code Goddess Prelude's Avatar
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    Functions do not nest. Move the definition of display_answer and display_menu outside of main.
    My best code is written with the delete key.

  3. #3
    Pig
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    Ahah! Thanks much.

  4. #4
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    Also note that you have infinate mutual recursion going on. While this is valid and clever in fancy functional proramming langauges, we don't do such things here in C++, here we are programming a computer, not solving lamda calculus. The C++ version would look something like this
    Code:
    int display_menu()
    {
    //...  as written
        int choice=0;
        cin>>choice;
        return choice;
    }
    
    void display_choice(int choice) 
    {
    //.. as written, but no display_menu()
    //.. no return 0; void functions do not need
    // .. a return, you can have one, but it's just
    // return; by itself.
    }
    
    int main() {
        for(int choice=display_menu(); choice != 0; choice = display_menu()) display_choice(choice);
        return 0;
    }
    The changes to the display_menu() have a mild amount of trickery. Here we rely on the fact that if a stream encounters bad input it does not change the value it's trying to write to. In our case if the user enters 'Q' in responce to the menu then display_menu() returns zero. We also have the side effects that cin.good() is false and we still have a 'Q' sitting in the input buffer, but we don't care about that right now. Stream driven menus are generally awkward to work with.

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