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c 的一些经典算法,满好的,适合初学者. 也可以当作小程序看,对初学者会很有帮助

 
输入一串字符，判断该字符串是不是合法的C语言标识符  
 
 

  
/*
 * Name: identifier.c
 * Author: x-bit, at www.patching.net, AllRights Reserved.
 * Description: 输入一串字符，判断该字符串是不是合法的C语言标识符。
 * Date: 09-05-2004
 * Compile environment: win2k+vc6下调试通过
 *
 */
#include <stdio.h>

int identf(char *str);
int isKey(char *str);
int x_strcmp(char *si, char *di);

int main()
{
 char buffer[256];
 printf("Enter a string: ");
 gets(buffer);
 if(identf(buffer))
  puts("合法的标识符");
 else
  puts("非法的标识符");
 
 return 0;
}

/**************************************************************************/
int identf(char *str)
{
 int flag=0;
 char *p=str;
 /*判断第一个字符是否符合*/
 if((*str>='a' && *str<='z') || (*str>='A' && *str<='Z') || *str=='_')
 {
  flag=1;
  str++;
 }
 /*从第二个字符开始遍历判断*/
 while(*str && flag)
 {
  if((*str>='a' && *str<='z') || (*str>='A' && *str<='Z') || *str=='_'
   || (*str>='0' && *str<='9'))
  {
   flag=1;
   str++;
  }
  else
   flag=0;
 }
 
 /*判断是不是关键字*/
 if(flag)
  flag=isKey(p);

 return flag;
}
/*****************************是不是关键字*******************************/
int isKey(char *str)
{
 char *keyword[]={"auto", "break", "case", "char", "const", "continue", "default",
     "do", "double", "else", "enum", "extern", "float", "for", "goto",
     "if", "int", "long", "register", "return", "short", "signed", 
     "sizeof", "static", "struct", "switch", "typedef", "union", "unsigned",
     "void", "volatile", "while"};
 int i, flag=1;

 for(i=0; i<32; i++)
 {
  if(x_strcmp(str, keyword[i])==0)
  {
   flag=0;
   break;
  }
 }

 return flag;
}
/*****************************字符串比较函数*******************************/
/* 为了练技术，自己写了一个strcmp() */
int x_strcmp(char *si, char *di)
{
 while(*si && *di && *si==*di)  /*两串都没结束，且*/
 {
  si++;
  di++;
 }

 return *si-*di;
}