调用函数fac计算值和求标准差的题目的问题

问题1：编写函数int fac(int x)计算x!的值。在主函数中输入n和m的值，通过调用函数fac计算Cnm的值？
回答：
求组合C(m,n)不能简单的用阶乘，会溢出
把C(m,n)展开为
C(m, n)=C(m, n-1)*(m-n+1)/n
和
C(m,n)=C(m-1,n-1)+C(m-1,n)
能避开数据溢出

#include 
using namespace std;
long int combination(int m, int n) {
  if(n == 1) {
    return m;
  }
  return combination(m, n - 1) * (m - n + 1) / n;
}


long int combination2(int m, int n) {
  if(n == 0 || m == n)
    return 1;
  return combination2(m - 1, n - 1) + combination2(m - 1, n);
}


int main() {
  int m, n;
  cout << "m=";
  cin >> m;
  cout << "n=";
  cin >> n;
  if(m < n) {
    cout << "无效输入" << endl;
    return 0;
  }
  cout << "组合:" << combination (m, n) << endl;
  cout << "组合:" << combination2 (m, n) << endl;
  return 1;
}

问题2：求标准差c语言程序看看哪里错了？
补充：

#include
#define MAXSIZE 100
main()
{
    int i,n;
    float value[MAXSIZE],d,s,ss,mean,v,st;
    //d-deviation s-sum ss-sumsqr,st-standard variance
    s=ss=n=0;
    printf("input values:input 0 to end\n");
    for(i=1;i

回答：

#include //补上
#include
#define MAXSIZE 100
int main() {
  int i, n;
  float value[MAXSIZE], d, s, ss, mean, v, st;
  //d-deviation s-sum ss-sumsqr,st-standard variance
  s = ss = n = 0;
  printf("input values:input 0 to end\n");
  for(i = 1; i < MAXSIZE; i++) {
    scanf("%f", &value[i]);//漏写&
    if(value[i] == 0)
      break;
    s += value[i];
    n++;
  }
  mean = s / (float)n;
  for(i = 1; i <= n; i++) {
    d = value[i] - mean;
    ss += d * d;
  }
  v = ss / (float)n;
  st = sqrt(v);
  printf("number of items:%d\n", n);
  printf("mean:%f\n", mean);
  printf("standard deviation:%f\n", st);
  return 0;
}