用字串處理很簡單#include <stdio.h>#include <string.h>void main (){ int n,i; char s[20]; scanf("%d", &n); sprintf(s,"%d", n); printf("%d\n",strlen(s)); for(i=strlen(s)-1;i>=0;i--){ printf("%c",s[i]); } printf("\n");}如果要用迴圈也可以的。補充：#include<stdio.h>void main(){long x;int temp=0,num=0;printf("請輸入一個整數:\n");scanf("%ld",&x);printf("它的每一位數字是:\n");while(x>0){printf("%3d",x%10);temp=temp*10+x%10;x=x/10;num++;}printf("\n它是一個%d位數.\n",num);printf("它的逆序是:%d\n",temp);}