1.c

#include <stdio.h>

typedef float matrix4x4_t[4][4];

static float matrix_det(const matrix4x4_t m)
{
    return
      m[0][3] * m[1][2] * m[2][1] * m[3][0] - m[0][2] * m[1][3] * m[2][1] * m[3][0] - m[0][3] * m[1][1] * m[2][2] * m[3][0]+m[0][1] * m[1][3] * m[2][2] * m[3][0] +
      m[0][2] * m[1][1] * m[2][3] * m[3][0] - m[0][1] * m[1][2] * m[2][3] * m[3][0] - m[0][3] * m[1][2] * m[2][0] * m[3][1]+m[0][2] * m[1][3] * m[2][0] * m[3][1] +
      m[0][3] * m[1][0] * m[2][2] * m[3][1] - m[0][0] * m[1][3] * m[2][2] * m[3][1] - m[0][2] * m[1][0] * m[2][3] * m[3][1]+m[0][0] * m[1][2] * m[2][3] * m[3][1] +
      m[0][3] * m[1][1] * m[2][0] * m[3][2] - m[0][1] * m[1][3] * m[2][0] * m[3][2] - m[0][3] * m[1][0] * m[2][1] * m[3][2]+m[0][0] * m[1][3] * m[2][1] * m[3][2] +
      m[0][1] * m[1][0] * m[2][3] * m[3][2] - m[0][0] * m[1][1] * m[2][3] * m[3][2] - m[0][2] * m[1][1] * m[2][0] * m[3][3]+m[0][1] * m[1][2] * m[2][0] * m[3][3] +
      m[0][2] * m[1][0] * m[2][1] * m[3][3] - m[0][0] * m[1][2] * m[2][1] * m[3][3] - m[0][1] * m[1][0] * m[2][2] * m[3][3]+m[0][0] * m[1][1] * m[2][2] * m[3][3];
}

int main(void)
{
    int i;
    matrix4x4_t mat = { 0 };
    printf("enter a 4x4 matrix line by line\n");
    for(i = 0; i < 4; i++)
        scanf("%f %f %f %f", &mat[i][0], &mat[i][1], &mat[i][2], &mat[i][3]);
    printf("D = %f\n", matrix_det(mat));
    return 0;
}