Typecasting questions...

This is a discussion on Typecasting questions... within the C++ Programming forums, part of the General Programming Boards category; Firstly, i made the following program that's supposed to convert an int to a char and back to an int. ...

  1. #1
    Not stupid, just stupider yaya's Avatar
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    Thumbs up Typecasting questions...

    Firstly, i made the following program that's supposed to convert an int to a char and back to an int. Why does it output a negative number?

    Code:
    #include <iostream>
    
    using namespace std;
    
    int main()
    {
        cout<<(int)((char)177);
        cin.get();
    }
    And secondly, why is it, on windows XP (not sure about vista) that the following program forces the computer to make a beeping sound?

    Code:
    #include <iostream>
    
    using namespace std;
    
    int main()
    {
        cout<<(char)7;
        cin.get();
    }
    Thanks

  2. #2
    The larch
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    1) For your compiler, char is apparently signed, 177 overflows, wraps around and becomes negative. Try unsigned char instead.

    2) ASCII characters with small values are "non-printing" characters, they were meant to represent actions, rather than character symbols. Char 7 happens to represent "Bell".

    Ascii table
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  3. #3
    Not stupid, just stupider yaya's Avatar
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    Thanks... but what exactly is "Bell"?

  4. #4
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    ASCII code 7, known as "BEL", is used by standard (aka console mode) applications to make a sound on the inbuilt speaker of the computer. It is normally used by programs to sound an audible beep.

  5. #5
    Kernel hacker
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    Quote Originally Posted by yaya View Post
    Thanks... but what exactly is "Bell"?
    It's the character that on a Teletype [typewriter style "terminal"] would ring a mechanical bell [like the end-of-line bell on a classic typewriter].

    You can actually make that sound "portable" by using the char '\a' (just like newline is '\n'). [I'm not sure there are any systems that actually DON'T use 7 as a BEL character, but there may be - I expect non-ASCII-based character sets, such as EBCDIC could do that].

    --
    mats
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  6. #6
    Not stupid, just stupider yaya's Avatar
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    Thanks everyone... I understand now

  7. #7
    C++まいる!Cをこわせ! Elysia's Avatar
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    On a side note, when using C++, you are advised to use C++ type-casting. They include dynamic_cast, static_cast, reinterpret_cast and const_cast (to my knowledge; not sure if there are more).
    You could read up a little about them or someone could explain it, I guess.
    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.

  8. #8
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    Quote Originally Posted by Elysia View Post
    On a side note, when using C++, you are advised to use C++ type-casting. They include dynamic_cast, static_cast, reinterpret_cast and const_cast (to my knowledge; not sure if there are more).
    You could read up a little about them or someone could explain it, I guess.
    Well, yeah. But rewriting the code in the original post to use C++-style casts has no effect on the question asked.

  9. #9
    C++まいる!Cをこわせ! Elysia's Avatar
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    Indeed, thus the side note
    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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