C语言杂记

• strcmp函数是可以和int数字进行比较的

   　　int ch[] = {, , , };
       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 = ;
  
       int sign = ;
  
       //跳过前面的空白字符
       while (*strp == ' ' || *strp == '\t' || *strp == '\n' || *strp == '\f' || *strp == '\b' || *strp == '\r')
           ++strp;
  
       if (*strp == '-') {
           sign = -;
           ++strp;
       } else if (*strp == '+') {
           sign = ;
           ++strp;
       }
  
       while ('' <= *strp && *strp <= '') {
  
           short c = (short) (*strp++ - '');
  
           //当前数字乘以乘数，得出补全0的高位
           result =  * 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=='\t'||x=='\n'||x=='\f'||x=='\b'||x=='\r')
     return ;
    else
     return ;
   }
   isdigit(int x)
   {
    if(x<=''&&x>='')
     return ;x`
    else
     return ;
  
   }
   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 = ;
  
           while (isdigit(c)) {
               total =  * total + (c - '');     /* accumulate digit */
               c = (int)(unsigned char)*nptr++;    /* get next char */
           }
  
           if (sign == '-')
               return -total;
           else
               return total;   /* return result, negated if necessary */
   }