C语言杂记

• strcmp函数是可以和int数字进行比较的
  

  1 　　int ch[] = {97, 97, 97, 0};
  
  2     puts(ch);
  
  3     if (strcmp("AAA", ch)) {
  
  4         printf("real?true!");
  
  5     }

   

• 实现stdlib::atoi函数(字符串转数字) 
  

   1 /**
  
   2 * 实现stdlib::atoi函数(字符串转数字)
  
   3 */
  
   4 int myatoi(const char *strp) {
  
   5 
  
   6     //用来存放最终值
  
   7     int result = 0;
  
   8 
  
   9     int sign = 1;
  
  10 
  
  11     //跳过前面的空白字符
  
  12     while (*strp == ' ' || *strp == '\t' || *strp == '\n' || *strp == '\f' || *strp == '\b' || *strp == '\r')
  
  13         ++strp;
  
  14 
  
  15     if (*strp == '-') {
  
  16         sign = -1;
  
  17         ++strp;
  
  18     } else if (*strp == '+') {
  
  19         sign = 1;
  
  20         ++strp;
  
  21     }
  
  22 
  
  23 
  
  24     while ('0' <= *strp && *strp <= '9') {
  
  25 
  
  26         short c = (short) (*strp++ - '0');
  
  27 
  
  28         //当前数字乘以乘数，得出补全0的高位
  
  29         result = 10 * result + c;
  
  30 
  
  31 
  
  32     }
  
  33     result *= sign;
  
  34 
  
  35     return result;
  
  36 }

   

  
  

•  下面是源代码，仔细看了一下，然后修改修改。

   1 isspace(int x)
  
   2 {
  
   3  if(x==' '||x=='\t'||x=='\n'||x=='\f'||x=='\b'||x=='\r')
  
   4   return 1;
  
   5  else  
  
   6   return 0;
  
   7 }
  
   8 isdigit(int x)
  
   9 {
  
  10  if(x<='9'&&x>='0')         
  
  11   return 1;x` 
  
  12  else 
  
  13   return 0;
  
  14 
  
  15 }
  
  16 int atoi(const char *nptr)
  
  17 {
  
  18         int c;              /* current char */
  
  19         int total;         /* current total */
  
  20         int sign;           /* if '-', then negative, otherwise positive */
  
  21 
  
  22         /* skip whitespace */
  
  23         while ( isspace((int)(unsigned char)*nptr) )
  
  24             ++nptr;
  
  25 
  
  26         c = (int)(unsigned char)*nptr++;
  
  27         sign = c;           /* save sign indication */
  
  28         if (c == '-' || c == '+')
  
  29             c = (int)(unsigned char)*nptr++;    /* skip sign */
  
  30 
  
  31         total = 0;
  
  32 
  
  33         while (isdigit(c)) {
  
  34             total = 10 * total + (c - '0');     /* accumulate digit */
  
  35             c = (int)(unsigned char)*nptr++;    /* get next char */
  
  36         }
  
  37 
  
  38         if (sign == '-')
  
  39             return -total;
  
  40         else
  
  41             return total;   /* return result, negated if necessary */
  
  42 }