#include <stdio.h>
#include <math.h>

int main(void)
{
    double A[4][4] = {
        { 3.8, 14.2, 6.3, -15.5 },
        { 8.3, -6.6, 5.8, 12.2 },
        { 6.4, -8.5, -4.3, 8.8 },
        { 17.1, -8.3, 14.4, -7.2 } };

    double B[4] = { 2.8, -4.7, 7.7, 13.5 };

    double X[4];
    double c;
    int s, i, j;
    int n = 4;

    double detA;

    for (s = 0; s < n - 1; s++)
    {
        for (i = s + 1; i < n; i++)
        {
            c = A[i][s] / A[s][s];
            B[i] = B[i] - c * B[s];
            for (j = s + 1; j < n; j++)
            {
                A[i][j] = A[i][j] - c * A[s][j];

            }
        }
    }

    X[n - 1] = B[n - 1] / A[n - 1][n - 1];

    for (i = n - 2; i >= 0; i--)
    {
        c = B[i];
        for (j = i + 1; j < n; j++)
        {
            c = c - A[i][j] * X[j];
        }
        X[i] = c / A[i][i];
    }

    printf("A:\n");
    for (i = 0; i < n; i++)
    {
        for (j = 0; j < n; j++)
        {
            printf("%f\t", A[i][j]);
        }
        printf("\n");
    }


    printf("X:\n");
    for (i = 0; i < n; i++)
    {
        printf("%f\t", X[i]);
    }
    printf("\n");

    detA = 1;
    for (i = 0; i < n; i++)
    {
        detA = detA * A[i][i];
    }

    printf("det(A): %f\n", detA);

    return 0;
}