C语言编程，求1！+2！+3！+......+20!,用到函数

#include double pasc(int);void main(){ int a = 20;double sum=0; do{ sum+=pasc(a); }while(--a); printf("%.0f",sum);}double pasc(int n){ printf("%d\n",n); if(n<2)return 1; return n*pasc(n-1);}