UVA - 10591Happy Number

当筵意气临九霄，星离雨散不终朝。这篇文章主要讲述UVA - 10591Happy Number相关的知识，希望能为你提供帮助。
Happy Number UVA - 10591
Let the sum of the square of the digits of a positive integer S0 be represented by S1. In a similar way, let the sum of the squares of the digits of S1 be represented by S2 and so on. If Si = 1 for some i ≥ 1, then the original integer S0 is said to be Happy number. A number, which is not happy, is called Unhappy number. For example 7 is a Happy number since 7 → 49 → 97 → 130 → 10 → 1 and 4 is an Unhappy number since 4 → 16 → 37 → 58 → 89 → 145 → 42 → 20 → 4.
Input
The input consists of several test cases, the number of which you are given in the first line of the input. Each test case consists of one line containing a single positive integer N smaller than 109.
Output
For each test case, you must print one of the following messages:
Case #p: N is a Happy number.
Case #p: N is an Unhappy number.
Here p stands for the case number (starting from 1).
You should print the first message if the number N is a happy number. Otherwise, print the second line.
Sample Input
3
7
4
13
Sample Output
Case #1: 7 is a Happy number.
Case #2: 4 is an Unhappy number.
Case #3: 13 is a Happy number.
这道题的递归或者说是循环我感觉挺好的，说实话第一遍我都没看懂这个题，就是给你一个数，如果这个数每个数字的平方和是1就是happy的，手动试了下，小于10的只有1满足，所以我只要把它平方和到一位数就行了，要不然这个循环走不出来，然后继续循环递归就行了

#include < stdio.h> int f(int b) { int s=0; while(b) { int t=b%10; s+=t*t; b/=10; } if(s< 10)return s; else return f(s); } int main() { int T; scanf("%d",& T); for(int i=1; i< =T; i++) { int x; scanf("%d",& x); printf("Case #%d: %d is a",i,x); if(f(x)==1) printf(" Happy number.\n"); else printf("n Unhappy number.\n"); } return 0; }

【UVA - 10591Happy Number】