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     unsigned int ans = 0;
  46     int valid = 1;
  47     int hexit;
  48
  49     // skip over 0x or 0X
  50     if (s[i] == '0') {
  51         ++i;
  52         if (s[i] == 'x' || s[i] == 'X') {
  53             ++i;
  54         }
  55     }
  56
  57     while (valid && s[i] != '\0') {
  58         ans = ans * 16;
  59         if (s[i] >= '0' && s[i] <= '9') {
  60             ans = ans + (s[i] - '0');
  61         } else {
  62             hexit = hex2int(s[i]);
  63             if (hexit == 0) {
  64                 valid = 0;
  65             } else {
  66                 ans = ans + hexit;
  67             }
  68         }
  69         ++i;
  70     }
  71
  72     if (!valid) {
  73         ans = 0;
  74     }
  75
  76     return ans;
  77 }
  78
  79 /* convert hex chars to integers return integer value */
  80 int hex2int(int h)
  81 {
  82     char options[] = { "AaBbCcDdEeFf" };
  83     int val = 0;
  84
  85     int i;
  86     for (i = 0; val == 0 && options[i] != '\0'; i++) {
  87         if (h == options[i]) {
  88             val = 10 + (i / 2);
  89         }
  90     }
  91
  92     return val;
  93 }
  94
  95
  96 int main()
  97 {
  98
  99     char *test[] =              // declare test as array of pointer to char
 100     {
 101         "0xf01",
 102         "0xA",
 103         "a",
 104         "0xB",
 105         "23",
 106         "100"
 107     };
 108
 109     int res = 0;
 110     int i = 0;
 111     for (i = 0; i < 6; i++) {
 112         res = htoi(test[i]);
 113         printf("%d\n", res);
 114     }
 115
 116     return 0;
 117 }