Passing an array to a function

This is a discussion on Passing an array to a function within the C Programming forums, part of the General Programming Boards category; Im trying to pass the array A into the function 'determinant' in order to calculate its determinant. However I keep ...

  1. #1
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    Passing an array to a function

    Im trying to pass the array A into the function 'determinant' in order to calculate its determinant. However I keep getting the following error: cannot convert `float (*)[((unsigned int)((int)x))]' to `float (*)[2]' for argument `1' to `float determinant(float (*)[2])'

    Here is my code:

    #include <stdio.h>

    float determinant(float a[2][2]);

    main ()
    {
    int col, row, x=2, y=2;
    float A[y][x], B[y],detA;


    printf("Enter Matrix A: ");

    for(row=0 ; row<y; row++)
    {
    for(col=0 ; col<x ; col++)
    scanf("%f", &A[row][col]);
    }

    printf("You entered:\n");

    for(row=0 ; row<y; row++)
    {
    for(col=0 ; col<x ; col++)
    printf("[%f]", A[row][col]);
    putchar('\n');
    }

    printf("Enter Matrix B: ");

    for(row=0 ; row<x; row++)
    scanf("%f", &B[row]);


    printf("You entered:\n");

    for(row=0 ; row<y; row++)
    printf("[%f]\n", B[row]);

    detA = determinant(A);
    printf("%f", detA);

    }


    /* Calculate determinant of matrix A */

    float determinant(float a[2][2])
    {
    float det;
    det = a[0][0]*a[1][1] - a[0][1]*a[1][0];
    return det;
    }


    Im editing and compiling using Dev-C++ 4.9.9.2
    Any help would be great, Thanks.

  2. #2
    C++ Witch laserlight's Avatar
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    The problem could be that you are inadvertently using variable length arrays. Examine:
    Code:
    int col, row, x=2, y=2;
    float A[y][x], B[y],detA;
    x and y are not constants, yet you use them to create A and B. Therefore, A and B are variable length arrays. As a quick fix, you could write:
    Code:
    float A[2][2], B[2], detA;
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  3. #3
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    Ah you're right, it works now when I replace x and y with 2.
    Thanks

  4. #4
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    i would of used a pointer for it and then passed the length of the x and y.

  5. #5
    C++まいる!Cをこわせ!
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    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.

  6. #6
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    Mostly the same code as before but I'm trying to use functions and calling by reference to input the matrices. But I'm still getting a similar error as before, and I can't see where I'm going wrong. Thanks.

    12 cannot convert `float (*)[2][2]' to `float* (*)[2]' for argument `1' to `void getmatrixA(float* (*)[2])'

    13 cannot convert `float (*)[2]' to `float**' for argument `1' to `void getmatrixB(float**)'

    Code:
    #include <stdio.h>
    
    void getmatrixA(float *A[2][2]);
    void getmatrixB(float *B[2]);
    float determinant(float a[2][2]);
    
    main ()
    {
         int col, row, x=2, y=2;
         float A[2][2], B[2], Ak[2][2], detA; 
         
         getmatrixA(&A);
         getmatrixB(&B);
         
         detA = determinant(A);
         printf("Determinant of A: %f\n", detA);
         
         for(row=0 ; row<y; row++)
         {
          for(col=0 ; col<x ; col++)
           {
            if(col=0)
            Ak[row][col]=B[row];
            else
            Ak[row][col]=A[row][col];
           }
         }
    
         printf("Ak:\n");
      
         for(row=0 ; row<y; row++)
         {
          for(col=0 ; col<x ; col++)
            printf("[%f]", Ak[row][col]);
          putchar('\n');
         }
    }
    
    void getmatrixA(float *A[2][2])
    {    
         int col, row;
         
         printf("Enter Matrix A: ");
         
         for(row=0 ; row<2; row++)
         { 
          for(col=0 ; col<2 ; col++)
            scanf("%f", &A[row][col]);
         }
    
         printf("You entered:\n");
      
         for(row=0 ; row<2; row++)
         {
          for(col=0 ; col<2 ; col++)
            printf("[%f]", A[row][col]);
          putchar('\n');
         }
    }
    
    void getmatrixB(float *B[2])
    {
         int col, row;
         
         printf("Enter Matrix B: ");
         
         for(row=0 ; row<2; row++)
          scanf("%f", &B[row]);
         
    
         printf("You entered:\n");
      
         for(row=0 ; row<2; row++)
            printf("[%f]\n", B[row]);
    }
          
    
    /* Calculate determinant of matrix A */ 
    
    float determinant(float a[2][2])
    {
      float det;          
      det = a[0][0]*a[1][1] - a[0][1]*a[1][0];
      return det;
    }

  7. #7
    C++まいる!Cをこわせ!
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    The types are wrong. You are trying to send x by y arrays to the functions, whose type should be float [x][y], not float* [x][y]. Furthermore, don't pass the address of the array. That would create a pointer to an array, float (*)[x][y], which is not the same as a pointer to the first element.
    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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