#include <stdio.h> int judge(char *strIp); int main() { char a[20]; while(1) { scanf("%s", a); if(0 == judge(a)) { printf("this is a correct ip\n"); } } } int judge(char *strIp) {
if(NULL == strIp)
{
return -1;
}
//IP must start with 0-9 if(*strIp > '9' || *strIp < '0') { return -1; } int num = 0; int dotNum = 0; do { if(*strIp >= '0' && *strIp <= '9') { num = 10 * num + *strIp - '0'; } else if(('.' == *strIp) || ('\0' == *strIp)) { //filter the string including '..' or ending with '.' if('.' == *(strIp - 1)) { return -1; } //filter the section number large than 255 or little than 0 if(num < 0 || num > 255) { return -1; } num = 0; //record the number of right dots if('.' == *strIp) { dotNum++; } } else { //Can't have chars excluding '0' - '9' and '.' return -1; } }while(*(strIp++)) if(3 == dotNum) { // ip is correct return 0; } else { //the string is too short for ip return -1; } }