#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>
int main() {
double x, pi, pi2, sum = 0.0,sum1=0.0,sum2=0.0,s=0.0 ; //sum1= sum over pi, sum2= sum over pi^2, s= standard deviation
int try, ntry, n, Nneed=100;
printf("Input the number of MC trials\n");
scanf("%d",&ntry);
srand((unsigned)time((long *)0));
for(n=0; n<Nneed ; n++) {
sum=0;
for (try = 0; try < ntry; try++) {
x = rand() / (double) RAND_MAX;
sum += 4.0 / (1.0 + x * x);
}
pi = sum / ntry;
sum1 += pi;
sum2 += pi*pi;
}
s=sqrt(sum2/Nneed-(sum1/Nneed)*(sum1/Nneed));
printf("MC estimate for PI = %f\n standard deviation=%f", pi, s);
return 0;
}
