Thread: Issue with random numbers

Code:

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

int xPosCalc(int sigmaMatter, int muMatter, int sigmaAntimatter, int muAntimatter, int xRand)
{
    xRand = rand() % 36;
    int xPosMatter = (1/(sigmaMatter*sqrt(2*M_PI)))*exp(-((xRand-muMatter)*(xRand-muMatter))/(2*(sigmaMatter*sigmaMatter)));
    int xPosAntimatter = (1/(sigmaAntimatter*sqrt(2*M_PI)))*exp(-((xRand-muAntimatter)*(xRand-muAntimatter))/(2*(sigmaAntimatter*sigmaAntimatter)));
    int xProbability = xPosMatter * xPosAntimatter;
    printf("Random variable is: %d", xRand);
    printf("\nProbability is: %d", xProbability);
}

int main(void)
{
    int sigmaMatter = 4.2;
    int muMatter = 27.0;
    int sigmaAntimatter = 6.0;
    int muAntimatter = 17.0;
    int xRand = 0.0;
    xPosCalc(sigmaMatter, muMatter, sigmaAntimatter, muAntimatter, xRand);
}

The problem is my random variable (restricted from 0-35) comes out as 29 every time I run the program, not a random number like I need. I'm guessing this is either a problem with the way I'm passing my variables (something I'm still learning) or a stack error.

I know my math can be simplified, but I don't think that is what's causing the current issue.

Is there a faster way to get pseudorandom numbers other than the time() function? For my program I need to calculate 5000 numbers as fast as possible, and if I get the pseudorandom number from time() it will calculate all 5000 numbers based on less than 5000 random numbers, if that makes sense

make sure you really want to seed with time(); if you do, your results will not be repeatable and it will be harder to track down problems in your calcs. an alternative to using time(), pass in an argument for the seed so you can make runs with different sets of random values but still have repeatable results.