Identifiers
Time Limit: 1000ms Memory limit: 65536K 有疑问？点这里^_^
题目描写叙述
Identifier is an important concept in the C programming language. Identifiers provide names for several language elements, such as functions, variables, labels, etc.
An identifier is a sequence of characters. A valid identifier can contain only upper and lower case alphabetic characters, underscore and digits, and must begin with an alphabetic character or an underscore. Given a list of chararcter sequences, write a program
to check if they are valid identifiers.
输入
The first line of the input contains one integer, N, indicating the number of strings in the input. N lines follow, each of which contains at least one and no more than 100 characters. (only upper and lower case alphabetic characters,
digits, underscore (" "), hyphen ("-"), period ("."), comma (","), colon (":"), semicolon (";"), exclamation mark ("!"), question mark ("?"), single and double quotation marks, parentheses, white space and square brackets may appear in the character sequences.)
digits, underscore (" "), hyphen ("-"), period ("."), comma (","), colon (":"), semicolon (";"), exclamation mark ("!"), question mark ("?"), single and double quotation marks, parentheses, white space and square brackets may appear in the character sequences.)
输出
For each of the N lines, output "Yes" (without quote marks) if the character sequence contained in that line make a valid identifier; output "No" (without quote marks) otherwise.
演示样例输入
7
ValidIdentifier
valid_identifier
valid_identifier
0 invalid identifier
1234567
invalid identifier
adefhklmruvwxyz12356790 -.,:;!?'"()[]ABCDGIJLMQRSTVWXYZ
演示样例输出
Yes
Yes
Yes
No
No
No
No
提示
来源
山东省第二届ACM大学生程序设计竞赛
解题思路：
推断是否输入的字符串为合法标识符。
代码：
#include <iostream>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
using namespace std;
string str[1000];
int main()
{
int n;cin>>n;
getchar();//必须得加这个,吸收空格，否则后面用getline会出错
for(int i=1;i<=n;i++)
{
getline(cin,str[i]);
bool ok=1;
int len=str[i].length();
if(!isalpha(str[i][0])&&str[i][0]!='_')//首字母不是字母也不是下划线
{
cout<<"No"<<endl;
continue;
}
for(int j=0;j<len;j++)
{
if(!isdigit(str[i][j])&&!isalpha(str[i][j])&&str[i][j]!='_')//不符合要求
{
ok=0;
break;
}
}
if(ok)
cout<<"Yes"<<endl;
else
cout<<"No"<<endl;
}
return 0;
}
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