2012北邮网研真题C-IP地址
题目
代码
//IP地址
#include <iostream>
#include <string.h>
using namespace std;
char a[20];
int main() {
int T;
cin >> T;
while(T--) {
memset(a, 0, sizeof(a)); //把字符数组初始为'\0' '\0'的ASCII是0
cin >> a;
int p = 0, start = 0, tmp = 0;
while(a[p] != '.' && p < 20) {
p++;
//cout << p << endl;
}
if(p == 0) {
cout << "No" << endl;
continue;
}
bool flag = true;
for(int i = 0; i < p; i++) {
if(a[i] < '0' || a[i] > '9') {
flag = false;
break;
}
tmp = tmp*10 + a[i]-'0';
}
if(tmp > 255 || tmp < 0 || flag == false) {
//cout << "11111111111111111" << endl;
cout << "No" << endl;
continue;
}
p++;
start = p;
tmp = 0;
flag = true;
while(a[p] != '.' && p < 20) {
p++;
}
if(p == start) {
cout << "No" << endl;
continue;
}
for(int i = start; i < p; i++) {
if(a[i] < '0' || a[i] > '9') {
flag = false;
break;
}
tmp = tmp*10 + a[i]-'0';
}
if(tmp > 255 || tmp < 0 || flag == false) {
//cout << "222222222222222222" << endl;
cout << "No" << endl;
continue;
}
p++;
start = p;
tmp = 0;
flag = true;
while(a[p] != '.' && p < 20) {
p++;
}
if(p == start) {
cout << "No" << endl;
continue;
}
for(int i = start; i < p; i++) {
if(a[i] < '0' || a[i] > '9') {
flag = false;
break;
}
tmp = tmp*10 + a[i]-'0';
}
if(tmp > 255 || tmp < 0 || flag == false) {
// cout << tmp << endl;
// cout << p << endl;
// cout << "33333333333333333333333" << endl;
cout << "No" << endl;
continue;
}
p++;
start = p;
tmp = 0;
flag = true;
while(a[p] != '\0' && p < 20) {
p++;
}
if(p == start) {
cout << "No" << endl;
continue;
}
for(int i = start; i < p; i++) {
if(a[i] < '0' || a[i] > '9') {
flag = false;
break;
}
tmp = tmp*10 + a[i]-'0';
}
if(tmp > 255 || tmp < 0 || flag == false) {
//cout << "4444444444444444" << endl;
cout << "No" << endl;
continue;
}
cout << "Yes" << endl;
}
return 0;
}
测试
我测试了用例1.1.1，我一直没想出来为什么程序判断出no。后来才发现是在初始化的时候是把字符数组设成了ASCII码0，对应的就是’\0’。因为迟迟没有找到那个“.”,所以此时p=20了，进入下面的for循环时，因为a[i]的值是’\0’，对应ASCII码是0，自然比‘0’要小，flag变为false，进入下面的if判断语句。