请教C语言编程题

#include "stdio.h"
void main()
{
int s,i,sum;
s=1;
sum=0;
for(i=1;i<=20;i++)
{
s=s*i;
sum=sum+s;
}
printf("%d\n",sum);
}

int main(void)
{
long int sum = 0;
for(int i=1; i<=10; i++)
{
int sum_i = 1;
for(int n=2; n<=i; ++n)
{
sum_i *= n;
}
printf("sum_%d=%ld\t", i, sum_i);
sum += sum_i;
}

printf("sum=%ld\n", sum);
return 0;
}

#include "stdio.h"
main()
{
int i,j;
double m,sum=0;
for(i=1;i<=20;i++)
{
{
for(m=1,j=1;j<=i;j++)
m=m*j;
}
sum=sum+m;
}
printf("\nsum=%le",sum);
}

数据比较大,所以用双精度数.

main(){
long sum = 1;
int n,m;
for(n = 1;n < 21;n++){