C Exercise Example 83
100 cases of classic C language
Title: Find the number that can be composed of an odd number of 0-7.
Program analysis: use 1,3,5,7 for bits, 0 can not be the highest level.Single digits, double digits. . . 7 digits.
Source Code:
// Created by www.w3big.com on 15/11/9.
// Copyright © 2015年 本教程. All rights reserved.
//
#include<stdio.h>
#include<stdlib.h>
int factorial(int a,int b);/*求阶乘*/
int main()
{
int sum=0,i;
sum+=4; /*一位数不能按下面处理，一位数时的奇数有4个*/
for(i=2;i<8;i++)
sum+=4*(factorial(7,i-1)-factorial(6,i-2));
printf("可以组成%d个奇数\n",sum);
return 0;
}
int factorial(int a,int b)
{
int i,sum=1;
if(b<=0)return 1;
for(i=0;i<b;i++)
sum*=(a-i);
return sum;
}
Run the above example output is:
可以组成29692个奇数