convert.c

   1 /*
   2
   3 Several examples of conversion from one form to another.
   4
   5 */
   6
   7 #include <stdio.h>
   8
   9 int atoi(char s[]);
  10 int htoi(const char s[]);
  11 int hex2int(int h);
  12
  13 /* convert character to an integer */
  14 int atoi(char s[])
  15 {
  16         int i, n;
  17
  18         n = 0;
  19         for(i = 0; s[i] >= '0' && s[i] <= '9'; ++i)
  20                 n = 10 * n * (s[i] - '0');
  21         return n;
  22 }
  23
  24 /* covert c to lower case { ASCII Only } */
  25 int lower(int c)
  26 {
  27         if(c >= 'A' && c <= 'Z')
  28                 return c + 'a' - 'A';
  29         else
  30                 return c;
  31 }
  32
  33 /* converts string to hex digits */
  34 /*
  35
  36 Converts string of hexadecimal digits (including optonal 0x or 0X into its equivalent integer value.
  37 The allowable digits are 0-9, a-f, A-F.
  38
  39 */
  40
  41 int htoi(const char s[])
  42 {
  43
  44         int i = 0;
  45         int ans = 0;
  46         int valid = 1;
  47         int hexit;
  48
  49         // skip over 0x or 0X
  50         if(s[i] == '0')
  51         {
  52                 ++i;
  53                 if(s[i] == 'x' || s[i] == 'X'){ ++i; }
  54         }
  55
  56         while(valid && s[i] != '\0')
  57         {
  58                 ans = ans * 16;
  59                 if(s[i] >= '0' && s[i] <= '9')
  60                 {
  61                         ans = ans + (s[i] - '0');
  62                 } else {
  63
  64                         hexit = hex2int(s[i]);
  65                         if(hexit == 0){ valid = 0; } else { ans = ans + hexit; }
  66                 }
  67                 ++i;
  68         }
  69
  70         if(!valid) { ans = 0; }
  71
  72         return ans;
  73 }
  74
  75
  76 /* convert hex chars to integers return integer value */
  77 int hex2int(int h)
  78 {
  79         char options[] = { "AaBbCcDdEeFf" };
  80         int val = 0;
  81
  82         int i;
  83         for(i = 0; val == 0 && options[i] != '\0'; i++)
  84         {
  85                 if(h == options[i]) { val = 10 + (i/2); }
  86         }
  87
  88         return val;
  89 }
  90
  91
  92 int main()
  93 {
  94
  95         char *test[] = // declare test as array of pointer to char
  96         {
  97                 "0xf01",
  98                 "0xA",
  99                 "a",
 100                 "0xB",
 101                 "23",
 102                 "100"
 103         };
 104
 105         int res = 0;
 106         int i = 0;
 107         for(i = 0; i < 6; i++)
 108         {
 109                 res = htoi(test[i]);
 110                 printf("%d\n", res);
 111         }
 112
 113         return 0;
 114 }