自然而然

#include<stdio.h>
#include<stdlib.h>
int main(int argc, char const *argv[])
{
    unsigned i,j,k=0,n=1e8;
    for(i=0;i<n;i++){
        for(j=0;j<RAND_MAX;j+=rand())
            k++;
    }
    printf("e=%f
", (double)k/n);
    return 0;
}

gcc e.c -O3&&./a.out

e=2.718259