Error in dynamically allocating memory in C

I am trying to calculate the determinant of an NxN matrix. 开发者_Python百科This piece of code gives an error in lines where I try to allocate the memory dynamically.

error: a value of type "int" cannot be assigned to an entity of type "float *"

error: a value of type "int" cannot be assigned to an entity of type "float **"

double CalcDeterminant( float **mat, int order)
{
    float **minor;
    unsigned short i;
    float det = 0;
    // order must be >= 0
    // stop the recursion when matrix is a single element
    if( order == 1 )
        return mat[0][0];

    // the determinant value
    // allocate the cofactor matrix

    **minor = malloc((order-1) * sizeof(float *));
    for(i=0;i<order-1;i++)
        minor[i] = malloc((order-1) * sizeof(float));**

    //float *mat2d = malloc( rows * cols * sizeof( float ));
    for(i = 0; i < order; i++ )
    {
        // get minor of element (0,i)
        GetMinor( mat, minor, 0, i , order);
        // the recusion is here!

        det += (i%2==1?-1.0:1.0) * mat[0][i] * CalcDeterminant(minor,order-1);
        //det += pow( -1.0, i ) * mat[0][i] * CalcDeterminant( minor,order-1 );
    }

    // release memory
    for(i=0;i<order-1;i++)
        free(minor[i]);
    free(minor);
    return det;
}

You need to add the line #include <stdlib.h> so that malloc() is properly declared.

As it stands, the compiler is being very lax (C89 mode) and allowing implicit function declarations, so when the compiler comes across malloc(), it assumes that it is a function that returns an int, instead of the correct void *.

You need to change your compilation options until the compiler complains more loudly. For example, if you use GCC, you should consider:

gcc -std=c99 -Wall -Wextra -Wstrict-prototypes -Wmissing-prototypes ...

You may prefer, or even need, to use -std=gnu99 instead -std=c99; that enables many extensions while still using the C99 core language. But using options along those lines and ensuring there are no compilation warnings is good discipline. Using -Werror enforces the discipline; it converts any warning message from the compiler into an error, so the compilation fails.

You need to include the header file stdlib.h.