pointer help

This is a discussion on pointer help within the C Programming forums, part of the General Programming Boards category; i need help with pointer iam just starting out can someone hep me. my program doesnt run [ Code: #include<stdio.h> ...

  1. #1
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    pointer help

    i need help with pointer iam just starting out can someone hep me. my program doesnt run

    [
    Code:
    #include<stdio.h>
    #include<conio.h>
    
    int f(int a, int b);
    main()
    {
          int a=2,b=4;
          int t;      
          
       t=  f(&a,&b);
         
         printf("%i %i",a,b);
         getchar(); 
    
    }
    int f(int *a, int *b)
    {
        int t;
       a=5;
       b=10;
       t=a+b;
       return t;
         
    }

  2. #2
    Registered User Char*Pntr's Avatar
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    EDIT:

    Arghhh! I screwed this up again! See cph's answer, it's better than mine.
    At least I got the de-reference part right.
    Last edited by Char*Pntr; 09-19-2010 at 11:06 AM.

  3. #3
    cph
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    Code:
    #include <stdio.h>
    
    void func (int *pa, int *pb)
    {
        int tmp = *pa;
    
        *pa = *pb;
        *pb = tmp;
    }
    
    int main (void)
    {
        int a = 2, b = 4;
    
        printf("%i %i\n", a, b);
        func(&a, &b);
        printf("%i %i\n", a, b);
    
        return(0);
    }

  4. #4
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by mouse666666
    i need help with pointer iam just starting out can someone hep me. my program doesnt run
    What is your program supposed to do in the first place?
    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

  5. #5
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    Apparently swap two variables.

  6. #6
    Registered User Char*Pntr's Avatar
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    Quote Originally Posted by mouse666666 View Post
    i need help with pointer iam just starting out can someone hep me. my program doesnt run

    [
    Code:
    #include<stdio.h>
    #include<conio.h>
    
    int f(int a, int b);
    main()
    {
          int a=2,b=4;
          int t;      
          
       t=  f(&a,&b);
         
         printf("%i %i",a,b);
         getchar(); 
    
    }
    int f(int *a, int *b)
    {
        int t;
       a=5;
       b=10;
       t=a+b;
       return t;
         
    }
    I take back what I said in my edit. The solution provided may work, but it also completely
    rewrote his function.

    Re-writing his code will not help him to learn, especially in this case when there
    was a very simple solution.

  7. #7
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by Syscal
    Apparently swap two variables.
    I suspect that "assign 5 and 10 to a and b in main from f and then print a and b in main" is more likely to be the answer. The fix I would then suggest is to dereference a and b in f. Still, we should wait and see what mouse666666 really had in mind.

    Incidentally, mouse666666: you should explicitly declare the main function as returning an int, and then return 0 at its end (optional in C99). It looks like you do not need the non-standard <conio.h> at all. Your indentation could be improved; look at cph's example in post #3 for inspiration.
    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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    Woops, I was reading cph's code, not the OP's. To fix his code:


    Code:
    #include<stdio.h>
    #include<conio.h>
    
    int f(int *a, int *b);
    int main(){
    
        int a=2,b=4, t;
    
        t = f(&a,&b);
    
        printf("%i %i",a,b);
        getchar();
    
        return 0;
    
    }
    int f(int *a, int *b){
      
       int t;
    
       *a=5;
       *b=10;
       t = *a + *b;
    
       return t;
    }
    OP: Your prototype wasn't the same as the formal parameters at the bottom. Also, you weren't dereferencing the pointers in your function.
    Last edited by Syscal; 09-19-2010 at 11:29 AM.

  9. #9
    cph
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    Quote Originally Posted by Char*Pntr View Post
    I take back what I said in my edit. The solution provided may work, but it also completely
    rewrote his function.

    Re-writing his code will not help him to learn, especially in this case when there
    was a very simple solution.
    I'm sure I was only providing the hint to mouse666666 (I hope I didn't overdo the hint )

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