第二届acm省赛C identifier 字符串操作

Identifiers

Time Limit: 1000ms   Memory limit: 65536K  有疑问？点这里^_^

题目描述

 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.)

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.

示例输入

7
ValidIdentifier
valid_identifier
valid_identifier
0 invalid identifier
1234567
invalid identifier
adefhklmruvwxyz12356790 -.,:;!?'"()[]ABCDGIJLMQRSTVWXYZ

示例输出

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：

判断是否输入的字符串为合法标识符。

1、字符序列的输入用到  getline(cin,st[i]);

2、在cin>>n 与 getline(cin,st[i]); 之间需要使用 getchar(); 获取输入输入n 之后的回车符。

3、string 与 char [] 类型函数使用不同。  int len =st[i].length();          int len=strlen(st[i]);

4、判断字符c是否为字母和数字的函数（头文件#include ），isalpha(c)  ,   isdigit(c)   是返回非零，不是返回零。

代码：

#include
#include
#include
#include
#include

using namespace std;

string st[10005];
int i,j,k;
int n;

int main()
{
    cin>>n;
    getchar();
    for(i=1;i<=n;i++)
    {
        getline(cin,st[i]);
//                    for(j=0;st[i][j]!='\0';j++)
//                    {
//                        cout< //                    }
//                    cout<         bool b1=1;
        int len=st[i].length();
        //cout<         //cout<         if(!isalpha(st[i][0]) && st[i][0]!='_')
        {
            cout<<"No"<             continue;
        }
        for(j=1;j         {
            if(!isalpha(st[i][j]) && st[i][j]!='_' && !isdigit(st[i][j]))
            {
                b1=0;
                break;
            }
        }
        if(b1)
        {
            cout<<"Yes"<         }
        else
            cout<<"No"<     }
    return 0;
}