ex_4-12.c

   1 #include <string.h>
   2 #include <stdio.h>
   3
   4 /* print contents of array */
   5 void print_array(char s[])
   6 {
   7         int i;
   8         for(i = 0; i < strlen(s); i++)
   9                 printf("%c", s[i]);
  10         printf("\n");
  11 }
  12
  13 /* reverse contents of array in place */
  14 void reverse_array(char s[])
  15 {
  16         int c, i, j;
  17         for(i = 0, j = strlen(s)-1; i < j; i++, j--)
  18         {
  19                 c = s[i];
  20                 s[i] = s[j];
  21                 s[j] = c;
  22         }
  23 }
  24
  25 /* convert int n into chars in s[] - page 64*/
  26 void itoa(int n, char s[])
  27 {
  28         int i, sign;
  29
  30         if((sign = n) < 0)      // record sign
  31                 n = -n;         // reverse sign
  32         i = 0;
  33         do {                            // generates digits in reverse order
  34                 s[i++] = n % 10 + '0';  // get next digit and load into array
  35         } while ((n /= 10) > 0);        // delete each digit as we move along
  36         if(sign < 0)
  37                 s[i++] = '-';
  38         s[i] = '\0';
  39         reverse_array(s);
  40 }
  41
  42 /* recursive version of itoa - book has not covered pointers yet :( */
  43 int itoa_rec(int n, char s[], int i)
  44 {
  45         if(n < 0)
  46         {
  47                 s[i++] = '-';
  48                 n = -n;
  49         }
  50         if(n / 10)
  51                 i = itoa_rec(n/10, s,i);
  52
  53         s[i++] = (n % 10 + '0');
  54         s[i] = '\0';
  55         return i;
  56 }
  57
  58 int main()
  59 {
  60         char s[10]; // must have plenty of space here...
  61         int n = -1024;
  62
  63         itoa(n, s);
  64         print_array(s);
  65
  66         itoa_rec(n, s, 0);
  67         print_array(s);
  68         return 1;
  69 }