C program to check if given matrix is a upper triangle

// Function to check matrix is in upper triangular
// form or not.
#include<stdio.h>
int N,N;
int isUpperTriangularMatrix(int mat[N][N])
{
    for (int i = 1; i < N; i++)
        for (int j = 0; j < i; j++)
            if (mat[i][j] != 0)
                return 0;
    return 1;
}

// Driver function.
int main()
{
    int N=N=4;
    int mat[4][4] = { { 1, 3, 5, 3 },
                      { 0, 4, 6, 2 },
                      { 0, 0, 2, 5 },
                      { 0, 0, 0, 6 } };
    if (isUpperTriangularMatrix(mat))
        printf( "Yes");
    else
        printf("No");
    return 0;
}