printing elements of an array using pointers

This is a discussion on printing elements of an array using pointers within the C Programming forums, part of the General Programming Boards category; Hi, I'm just learning about pointers and as a simple exercise I am trying to print the elements of the ...

  1. #1
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    printing elements of an array using pointers

    Hi,

    I'm just learning about pointers and as a simple exercise I am trying to print the elements of the array. I'm trying to write a simple function that cycles through the columns and then prints each value to the screen. However, I'm having trouble calling the function properly.

    Code:
    /*Function the prints a single row array's contents to the screen. */
    
    void  matrix_print(int row, int col, double *m){
      int i;
      for(i=0; i<col; i++){
       
        printf("%d  ",*(m+i*col));
      }
      printf("\n");
    }
    
    main(){
    
      double arr[5] = { 2.5, 3.2, 18.7, -1.35, 4.2 };
      matrix_print(1, 5, *arr[5]);  //causing an error
    }
    The problem in the 3rd argument to the of the matrix_print. The error says that it is an compatible type. Any suggestions?

    Thanks in advance!

  2. #2
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    your function expects a pointer to a double
    you are passing in a double (located outside the bounds of arr)
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  3. #3
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    Code:
        matrix_print(1, 5, arr);
    and
    Code:
        for (i = 0; i < col; i++)   
            printf("%g  ",*(m+row*i));
        putchar('\n');
    this will print col elements from row (from m)

  4. #4
    cas
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    You're trying to make pointers more complex than they really are. C scales pointer arithmetic, so you don't need to calculate indices. There are two obvious ways to print out your array:
    Code:
    #include <stdio.h>
    
    static void f(double *a, int n)
    {
      int i;
    
      for(i = 0; i < n; i++)
      {
        printf("%f ", a[i]);
        /* or slightly less obvious, imo */
        printf("%f ", *(a + i));
      }
      putchar('\n');
    }
    
    int main(void)
    {
      double a[5] = { 2.5, 3.2, 18.7, -1.35, 4.2 };
    
      f(a, 5);
    
      return 0;
    }
    You can use the array subscript operator (that is, []) on pointers. Arrays and pointers have a close relationship in C, which means that often you can treat them the same way. In fact, the following function declaration:
    Code:
    void f(double a[]);
    is the same as:
    Code:
    void f(double *a);
    Don't get the idea that pointers and arrays are the same thing--they're not--but their relationship is such that you can use the array operator on pointers (and, to tell the truth, you can only use it on pointers, but that's another discussion).

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