用子程序和过程文件编制程序 M!/(M-N)!*N! 且M>N

#include "stdio.h"
long fac(int a)
{
long n;
if(a==0)n=1;
else
if(a==1)n=1;
else
n=fac(a-1)*a;
return(n);
}
main()
{
int m,n;
long t;
printf("please input m and n(m>n):");
scanf("%d%d",&m,&n);
while(m<n)
{
printf("input error!\n");
printf("please input m and n(m>n):");
scanf("%d%d",&m,&n);
}
t=fac(m)/fac(m-n)/fac(n);
printf("%d!/[(%d-%d)!*%d!]=%ld",m,m,n,n,t);
}

/*运行结果：
please input m and n(m>n):5 3
5!/[(5-3)!*3!]=10
*/