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  1. #include <stdio.h>
  2. #include <limits.h>
  3.  
  4. static void reverse(char* buf, size_t size)
  5. {
  6.   for (size_t i = 0; i < size/2; ++i) {
  7.     // swap i <-> (size - i - 1)
  8.     char temp = buf[i];
  9.     buf[i] = buf[size - i - 1];
  10.     buf[size - i - 1] = temp;
  11.   }
  12. }
  13.  
  14.  
  15. static int to_binary_unsigned(unsigned int x, char* buf, size_t size)
  16. {
  17.   if (!buf || size < 2)
  18.     return -1; // error
  19.  
  20.   buf[0] = '\0';
  21.   size_t i = 1;
  22.   for ( ; i < size; ++i) {
  23.     buf[i] = "01"[x & 1];
  24.     x >>= 1;
  25.     if (x == 0)
  26.       break;
  27.   }
  28.   if (i == size)
  29.     return -1; // error
  30.   reverse(buf, i + 1);
  31.   return 0; // success
  32. }
  33.  
  34. static int to_binary(int x, char* buf, size_t size)
  35. {
  36.   if (x < 0) {
  37.     if (buf && size > 2)
  38.       *buf = '-'; // write sign
  39.     else
  40.       return -1; // error
  41.     return to_binary_unsigned(-(unsigned int)x, buf+1, size-1);
  42.   }
  43.   return to_binary_unsigned(x, buf, size);
  44. }
  45.  
  46.  
  47. int main(void)
  48. {
  49.   int x;
  50.   scanf("%d", &x);
  51.   char buf[2 + CHAR_BIT * sizeof x]; // sign + null + binary digits
  52.   to_binary(x, buf, sizeof buf);
  53.   puts(buf);
  54. }
Success #stdin #stdout 0s 9416KB
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https://ideone.com/d34jIP
language:
C (gcc 8.3)
created:
6 years ago
visibility:
secret

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