参考：

#include <stdio.h>

int main()
{
    int i, j;
    double c;
    double sum = 0.0;
    for (i = 1; i <= 20; i++)
    {
        c = 1;
        for (j = 1; j <=i ; j++)
        {
            c *= j;
        }
        sum += c;
    }
    printf("1+2!+3!+...+20!的和为：%lf\n", sum);
    // system("pause");
    return 0;
}

参考方法：

#include<stdio.h>
double Fun(double n)
{
    if(n == 0)
        return 1;
    else
        return n*Fun(n - 1);
}
int main(void)
{
    double sum = 0, i;
    for(i = 1;i <= 20; i++)
    {
        sum += Fun(i);
    }
    printf("%lf\n",sum);
    return 0;
}

参考方法：

#include <stdio.h>
#pragma warning(disable:4996)

void compute(long int);//计算前N!和的子函数

int main()
{
    long int number = 0;
    
    printf("求N!,请输入N;\n");
    scanf("%ld",&number);
    compute(number);//调用子函数

    //system("pause");
}

void compute(long int number)
{
    long int n = 1;
    long int sum = 0;
    long int i = 0;

    for(i = 0;i<number;++i)
    {
        n = n*(i+1);//计算当前的N!
        sum = sum + n;//计算前N!的和
        if(i<number-1) printf("%ld!+",i+1);
        if(i == number-1) printf("%ld!=%ld\n",i+1,sum);
    }
    
}