C++ Benchmark Code Crashing - long numbers - c++

Question

Beginner here...
Doing a code to check language performance in Cpp, Java and Python.
The code must generate a random number N (1-60), fill a NxN matrix with random numbers between 0 and 9 and calculate its determinant.
I started with cpp, but sometimes it succeeds, sometimes it fails. My guess is that crashes are related to bigger than "long long int" numbers. Can you guys please check my code?
GNU GCC / CodeBlocks.
Thanks,
Guile.
#include <iostream>
#include <time.h>
using namespace std;
struct Mat{
int N = 2;
int mat[60][60];
long long int det;
};
void setSize(Mat *Size){
srand (time(NULL));
do {
Size->N = rand()%60;
}
while (Size->N < 1);
}
void setMatrix (Mat *mat){
srand (time(NULL));
for (int i = 0; i < mat->N; i++){
for (int j = 0; j < mat->N; j++){
mat->mat[i][j] = rand()%10;
}
}
}
void det(Mat *m1){
int i, j, k;
long long int Ratio;
long long int determinant;
for(i = 0; i < m1->N; i++){
for(j = 0; j < m1->N; j++){
if(j>i){
Ratio = m1->mat[j][i]/m1->mat[i][i];
for(k = 0; k < m1->N; k++){
m1->mat[j][k] -= Ratio * m1->mat[i][k];
}
}
}
}
determinant = 1;
for(i = 0; i < m1->N; i++)
determinant *= m1->mat[i][i];
m1->det = determinant;
}
int main (void){
Mat M1;
setSize(&M1);
setMatrix (&M1);
det(&M1);
cout<<"Matrix size: "<<M1.N<<endl;
cout<<"Matrix determinant: "<<M1.det<<"\n\n";
return 0;
}

Answer 1

Inside your function setMatrix:
for (int j = 0; j < mat->N; j++){
mat->mat[i][j] = rand()%10;
}
rand() % 10 can sometimes generate 0 as well, thus putting zeroes inside your matrix. This will cause a floating-point exception when you do:
Ratio = m1->mat[j][i]/m1->mat[i][i];
This line will again cause an issue when you do
m1->mat[j][k] -= Ratio * m1->mat[i][k];
which can again set a zero in your matrix at mat[j][k] later which can become the denominator again, causing the floating-point exception.