Thread: Could someone please point me in the right direction ~ basic structs and funtions

  1. #1
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    Could someone please point me in the right direction ~ basic structs and funtions

    The exercise specifically asks for char parameters in the create_colour function for some reason.

    I'm getting a compiler error along the lines of invalid conversion from 'char' to 'char' which i'm also unclear on.

    Any help appreciated, thanks!

    Code:
    #include <stdio.h>
    
    
    struct colour{
      char red;
      char green;
      char blue;
    
    
      };
    
    
    struct colour create_colour(char r, char b, char g);
    void printcolour(struct colour a);
    
    
    int main(void)
    {
    
    
    struct colour red = create_colour(255, 0, 0);
    
    
    //struct colour green =create_colour(0, 255, 0);
    //struct colour blue =create_colour(0, 0, 255);
    //struct colour yellow =create_colour(255, 255, 0);
    //struct colour pink =create_colour(255, 0, 127);
    
    
    printcolour(red);
    
    
    return 0;
    }
    
    
    struct colour create_colour(char r, char b, char g)
    {
    
    
      struct colour x;
      sprintf(x.red, r);
      sprintf(x.green, g);
      sprintf(x.blue, b);
    
    
      return x;
    
    
    }
    
    
    void printcolour(struct colour a)
    {
      printf("RGB: %c, %c, %c\n", a.red, a.green, a.blue);
    }

  2. #2
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    What is the exact error message? Copy and paste it here; don't type it out.

  3. #3
    and the hat of int overfl Salem's Avatar
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    > sprintf(x.red, r);
    Yeah, these aren't going to work.

    Code:
    struct colour create_colour(char r, char b, char g)
    {
      struct colour x;
      x.red = r;
      x.green = g;
      x.blue = b;
      return x;
    }
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  4. #4
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    Thanks for the responses, so i've updated it and now it runs, however its not printing the values I thought I had saved into the red colour struct in the main function, instead it's just printing blanksCould someone please point me in the right direction ~ basic structs and funtions-aaaaaaaaaaaa-png
    updated code:
    Code:
    #include <stdio.h>
    
    
    struct colour{
      char red;
      char green;
      char blue;
    
    
      };
    
    
    struct colour create_colour(char r, char b, char g);
    void printcolour(struct colour a);
    
    
    int main(void)
    {
    
    
    struct colour red = create_colour(255, 0, 0);
    
    
    //struct colour green =create_colour(0, 255, 0);
    //struct colour blue =create_colour(0, 0, 255);
    //struct colour yellow =create_colour(255, 255, 0);
    //struct colour pink =create_colour(255, 0, 127);
    
    
    printcolour(red);
    
    
    return 0;
    }
    
    
    struct colour create_colour(char r, char b, char g)
    {
    
    
      struct colour x;
      x.red = r;
      x.green = g;
      x.blue = b;
    
    
      return x;
    
    
    }
    
    
    void printcolour(struct colour a)
    {
      printf("RGB: %c, %c, %c\n", a.red, a.green, a.blue);
    }

  5. #5
    and the hat of int overfl Salem's Avatar
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    Try printing them with %d instead of %c.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  6. #6
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    Now the output displays "RGB: -1, 0, 0" instead of the desired 255, 0, 0

  7. #7
    C++ Witch laserlight's Avatar
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    Whether char is signed or unsigned is implementation defined, and it looks like it is signed in this case, hence 255 is converted to -1. I would change to use unsigned char instead of char since that makes it explicit that you want unsigned char.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  8. #8
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    Wow we won! I read on google somewhere that the char would be unsigned by default but I guess not.. Thanks!

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