4-6

#include<stdio.h>
double fact(int n);
int main(void)
{
    int i;
    double sum;
    sum=0;
    for(i=1;i<=100;i++)
        sum=sum+fact(i);
    printf("1!+2!+...+100!=%e\n",sum);

    return 0;
}
double fact(int n)
{
    int i;
    double result;

    result=1;
    for(i=1;i<=n;i++)
        result=result*i;

    return result;
}