Howto compute the factorial of x

Question

how to get the value of an integer x, indicated by x!, it is the product of the numbers 1 to x.

Example: 5! 1x2x3x4x5 = 120.

Answer 1

You can simply do:

for(b = 1; b <= a; b++) {
  d *= b;
}
// d now has a!