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Swap function and pointers

This is a discussion on Swap function and pointers within the C Programming forums, part of the General Programming Boards category; Code: #include <stdio.h> void swap1(int, int); void swap2(int*, int*); int main() { int i = 1, j = 2; swap1(i, ...

  1. #1
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    Swap function and pointers

    Code:
    #include <stdio.h>
    void swap1(int, int);
    void swap2(int*, int*);
    int main()
    {
          int i = 1, j = 2;
          swap1(i, j);
          printf("%d and %d\n", i, j); /* For Problem #57 */
          swap2(&i, &j);
          printf("%d and %d\n", i, j); /* For Problem #58 */
          return 0;
    }
    void swap1(int i, int j)
    {
          int tmp = i;
          i = j;
          j = tmp;
    }
    void swap2(int *i, int *j)
    {
          int tmp = *i;
          *i = *j;
          tmp = *j;
    }
    According to my instructor, the first printf should output "1 and 2" and the 2nd printf will output "2 and 2". I'm not seeing it. I thought the first one would swap them and output "2 and 1", and as for the second printf, I have no idea how to work with these pointers. Any help will be greatly appreciated.

  2. #2
    Registered User manasij7479's Avatar
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    Manasij Mukherjee | gcc-4.9.2 @Arch Linux
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  3. #3
    and the hat of int overfl Salem's Avatar
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    > According to my instructor, the first printf should output "1 and 2" and the 2nd printf will output "2 and 2".
    What you need is a new instructor if they seriously think 2 and 2 is the result.

    First one does nothing to the variables, and the second one swaps.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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    thanks guys, I think I get it now.

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    Quote Originally Posted by Salem View Post
    First one does nothing to the variables, and the second one swaps.
    Look carefully at the swap2() function in the OP, Salem. It does not swap. The instructor is correct about what output would be produced.
    Salem likes this.
    Right 98% of the time, and don't care about the other 3%.

    If I seem grumpy or unhelpful in reply to you, or tell you you need to demonstrate more effort before you can expect help, it is likely you deserve it. Suck it up, Sunshine, and read this, this, and this before posting again.

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    Quote Originally Posted by grumpy View Post
    Look carefully at the swap2() function in the OP, Salem. It does not swap. The instructor is correct about what output would be produced.
    Unfortunatly, that's because the swap function is incorrect.

    Where did they get THIS teacher?

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