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  1. #include <stdio.h>
  2. #include <string.h>
  3. #include <stdlib.h>
  4.  
  5. typedef unsigned uint;
  6.  
  7. int chhex2val(char ch)
  8. {
  9.   if (ch >= '0' && ch <= '9')
  10.     return ch - '0';
  11.   if (ch >= 'A' && ch <= 'F')
  12.     return ch - 'A' + 10;
  13.   if (ch >= 'a' && ch <= 'f')
  14.     return ch - 'a' + 10;
  15.   abort();
  16.   return 0;
  17. }
  18.  
  19. char val2chhex(int v)
  20. {
  21.   if (v >= 0 && v < 16)
  22.     return "0123456789ABCDEF"[v];
  23.   abort();
  24.   return '0';
  25. }
  26.  
  27. // Multiplies a hex string like "17F" by 10 and
  28. // returns a string with the product (e.g. "0EF6").
  29. // The original string isn't modified.
  30. char* mulh10(char* h)
  31. {
  32.   size_t l = strlen(h);
  33.   char* p = malloc(l + 1 + 1);
  34.   size_t i;
  35.   uint c = 0;
  36.  
  37.   if (p == NULL)
  38.     abort();
  39.  
  40.   p[l + 1] = '\0';
  41.   for (i = 0; i < l; i++)
  42.   {
  43.     c += chhex2val(h[l - 1 - i]) * 10;
  44.     p[l - i] = val2chhex(c % 16);
  45.     c /= 16;
  46.   }
  47.   p[0] = val2chhex(c);
  48.  
  49.   return p;
  50. }
  51.  
  52. // Adds (arithmetically) to a hex string like "17F" a hex/dec digit, e.g. '9'.
  53. // Returns the modified original string (e.g. "188").
  54. char* addhd(char* h, char d)
  55. {
  56.   size_t l = strlen(h);
  57.   size_t i;
  58.   uint c = chhex2val(d);
  59.  
  60.   for (i = 0; c && i < l; i++)
  61.   {
  62.     c += chhex2val(h[l - 1 - i]);
  63.     h[l - 1 - i] = val2chhex(c % 16);
  64.     c /= 16;
  65.   }
  66.  
  67.   return h;
  68. }
  69.  
  70. int main(void)
  71. {
  72.   char num[] = "17F";
  73.   printf("\"17F\" (hex) * 10 = \"%s\" (hex)\n", mulh10(num));
  74.   printf("\"17F\" (hex) + '9' = \"%s\" (hex)\n", addhd(num, '9'));
  75.   printf("\"65535\" (dec) = \"%s\" (hex)\n",
  76.          addhd(mulh10(addhd(mulh10(addhd(mulh10(addhd(mulh10(addhd(mulh10(
  77.          "0"), '6')), '5')), '5')), '3')), '5'));
  78.   return 0;
  79. }
  80.  
Success #stdin #stdout 0.01s 1808KB
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stdin
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Standard input is empty
stdout
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"17F" (hex) * 10 = "0EF6" (hex)
"17F" (hex) + '9' = "188" (hex)
"65535" (dec) = "00FFFF" (hex)
https://ideone.com/aZZFw
language:
C99 (gcc 8.3)
created:
11 years ago
visibility:
public

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