Zhejiang University Edition "C Language Programming (3rd Edition)" Exercise 2-18

Exercise 2-18 Find the number of combinations (15 points)

This question requires writing a program to calculate the number of combinations of m elements (m≤n) from n different elements according to the formula .
It is recommended to define and call the function fact (n) to calculate n !, where the type of n is int and the function type is double.

Input format:
Enter two positive integers m and n (m≤n) in one line, separated by spaces.

Output format: output
according to the format "result = combination number calculation result". The title guarantees that the result is within the double type.

Sample input:

2 7

Sample output:

result = 21

Code:

#include"stdio.h"
double fact(int n)
{
    if(n >= 2)
    {
        return n*fact(n-1);
    }
    return 1;
}

int main()
{
    int m, n;
    scanf("%d %d", &m, &n);
    printf("result = %0.lf", fact(n)/fact(m)*fact(n-m)));
    return 0;
}

The above fact function is recursive. If you don't understand it, you can use Baidu.