long long fac(int m) { long long res = 1; for (int i = 1; i <= m; i++) { res *= i; } return res;}

The code written is incomplete and contains a logical error in the for loop.

The for loop should have the increment operator (i++) to increase the value of i in each iteration.

The corrected code is as follows:

long long fac(int m) {
long long res = 1;
for (int i = 1; i <= m; i++) {
res *= i;
}
return res;
}

This code calculates the factorial of a given integer 'm' using a for loop. It initializes the variable 'res' to 1 and multiplies it by every integer from 1 to the given integer 'm'. The final result is then returned.