C語言雜記

• strcmp函數是能夠和int數字進行比較的
  

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

   

• 實現stdlib::atoi函數(字符串轉數字) 
  

   1 /**
   2 * 實現stdlib::atoi函數(字符串轉數字)
   3 */
   4 int myatoi(const char *strp) {
   5 
   6     //用來存放最終值
   7     int result = 0;
   8 
   9     int sign = 1;
  10 
  11     //跳過前面的空白字符
  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         //當前數字乘以乘數，得出補全0的高位
  29         result = 10 * result + c;
  30 
  31 
  32     }
  33     result *= sign;
  34 
  35     return result;
  36 }

   

  
  

•  下面是源代碼，仔細看了一下，而後修改修改。

   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 }