Why doesn't this work?

This is a discussion on Why doesn't this work? within the C++ Programming forums, part of the General Programming Boards category; Hello Code: int main() { string str; str = "01"; if(str[0] == "0") cout << "Equal"; } Error: ISO C++ ...

  1. #1
    Registered User
    Join Date
    Feb 2010
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    67

    Smile Why doesn't this work?

    Hello

    Code:
    int main()
    {
        string str;
        str = "01";
        if(str[0] == "0")
            cout << "Equal";
    }
    Error:
    ISO C++ forbids comparison between pointer and integer

    How does one make it so that str[0] refers to the actual character with a string datatype to it?

  2. #2
    Registered User
    Join Date
    Jul 2010
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    26
    "0" is a C-style string, not a char. Use single quotes for char - '0'.

  3. #3
    C++まいる!Cをこわせ! Elysia's Avatar
    Join Date
    Oct 2007
    Posts
    22,602
    This error message is a bit misleading. But it makes perfect sense. Here's what happens:
    [0] fetches a specific element of the string, a character, which is of type char. The char is promoted to an integer before being compared.
    "0" is a C-style string, an array of two chars, which decays to a pointer const char*.
    So in the end, you try to compare an int with a const char* and that is why the compiler complains the way it does.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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