C语言杂记

• strcmp函数是可以和int数字进行比较的
  

  　　int ch[] = {97, 97, 97, 0};
      puts(ch);
      if (strcmp("AAA", ch)) {
          printf("real?true!");
      }

• 实现stdlib::atoi函数(字符串转数字) 
  

  /**
  * 实现stdlib::atoi函数(字符串转数字)
  */
  int myatoi(const char *strp) {
  
      //用来存放最终值
      int result = 0;
  
      int sign = 1;
  
      //跳过前面的空白字符
      while (*strp == ' ' || *strp == '	' || *strp == '
  ' || *strp == 'f' || *strp == '' || *strp == '
  ')
          ++strp;
  
      if (*strp == '-') {
          sign = -1;
          ++strp;
      } else if (*strp == '+') {
          sign = 1;
          ++strp;
      }
  
  
      while ('0' <= *strp && *strp <= '9') {
  
          short c = (short) (*strp++ - '0');
  
          //当前数字乘以乘数，得出补全0的高位
          result = 10 * result + c;
  
  
      }
      result *= sign;
  
      return result;
  }

  
  

•  下面是源代码，仔细看了一下，然后修改修改。

  isspace(int x)
  {
   if(x==' '||x=='	'||x=='
  '||x=='f'||x==''||x=='
  ')
    return 1;
   else  
    return 0;
  }
  isdigit(int x)
  {
   if(x<='9'&&x>='0')         
    return 1;x` 
   else 
    return 0;
  
  }
  int atoi(const char *nptr)
  {
          int c;              /* current char */
          int total;         /* current total */
          int sign;           /* if '-', then negative, otherwise positive */
  
          /* skip whitespace */
          while ( isspace((int)(unsigned char)*nptr) )
              ++nptr;
  
          c = (int)(unsigned char)*nptr++;
          sign = c;           /* save sign indication */
          if (c == '-' || c == '+')
              c = (int)(unsigned char)*nptr++;    /* skip sign */
  
          total = 0;
  
          while (isdigit(c)) {
              total = 10 * total + (c - '0');     /* accumulate digit */
              c = (int)(unsigned char)*nptr++;    /* get next char */
          }
  
          if (sign == '-')
              return -total;
          else
              return total;   /* return result, negated if necessary */
  }