test 1：一块钱的兑换方案

#include <stdio.h>
int main()
{
    
    
    //一块钱的兑换方案：可换为5毛，2毛，1毛
    int a, b, c, sum, count = 0;
    for (a = 0; a <= 2; a ++)//关键点：循环的选取
        for (b = 0; b <= 5; b ++)
            for (c = 0; c <= 10; c ++)
            {
    
    
                sum = a * 5 + b * 2 + c;
                if (sum == 10)
                {
    
    
                    count ++;
                    printf("%d个5毛，%d个2毛，%d个1毛\n", a, b, c);
                    break;
                }
            }
    printf("共有%d种兑换方案。\n", count);
    return 0;
}