IP判断 （C语言代码）初学者思路-易懂-_-

#include<stdio.h>
#include"string.h"
int main()
{
    char c[17];
    while(scanf("%s",c)!=EOF)
    {
        int num[4]={0},i=0,j,flag=1;
            for(j=0;j<4;j++)
            {
            while(c[i]!='.'&&c[i]!='\0')
            {
                if(c[i]>='0'&&c[i]<='9')
                {
                num[j]=num[j]*10+c[i]-'0';
                i++;
                }
                else
                {
                    printf("N\n");
                    flag=0;
                    break;
                 }
             }
             if(num[j]<0||num[j]>255) {flag=0; printf("N\n");break;}
             i++;
             if(flag==0) break;
            }
            if(flag==1) printf("Y\n");
        }
    return 0;
}