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  1. #include <stdio.h>
  2. #define is_upper(c)  ((c) >= 'A' && (c) <= 'Z')
  3. #define is_lower(c)  ((c) >= 'a' && (c) <= 'z')
  4. char* cesar_code(int k, char* s);
  5. char* cesar_decode(int k, char* s);
  6.  
  7.  
  8. int main(void){
  9. 	char s[] = "ABCDEF Hello World !!! END zero (XYZ)";
  10. 	int    k = 15;
  11.  
  12. 	printf("source str: %s\n", s);
  13. 	printf("coder  str: %s\n", cesar_code(k, s) );
  14. 	printf("decode str: %s\n", cesar_decode(k, s) );
  15. 	return 0;
  16. }
  17.  
  18. //шифратор
  19. char* cesar_code(int k, char* s){
  20. 	int   i;
  21. 	char* t = s;
  22.  
  23. 	k %= 26;
  24. 	if(k < 0)
  25. 		k = -k;
  26.  
  27. 	for(; *s; ++s){
  28. 		if(is_lower(*s)){
  29. 			i  = (*s - 'a' + k) % 26;
  30. 			*s = 'a' + i;
  31. 		} else if(is_upper(*s)){
  32. 			i  = (*s - 'A' + k) % 26;
  33. 			*s = 'A' + i;
  34. 		}
  35. 	}
  36. 	return t;
  37. }
  38.  
  39. //дешифратор
  40. char* cesar_decode(int k, char* s){
  41. 	int   i;
  42. 	char* t = s;
  43.  
  44. 	k %= 26;
  45. 	if(k < 0)
  46. 		k = -k;
  47.  
  48. 	for(; *s; ++s){
  49. 		if(is_lower(*s)){
  50. 			i = *s - 'a' - k;
  51. 			if(i < 0)
  52. 				i += 26;
  53. 			*s = 'a' + i;
  54. 		} else if(is_upper(*s)){
  55. 			i = *s - 'A' - k;
  56. 			if(i < 0)
  57. 				i += 26;
  58. 			*s = 'A' + i;
  59. 		}
  60. 	}
  61. 	return t;
  62. }
  63.  
Success #stdin #stdout 0s 2156KB
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stdin
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Standard input is empty
stdout
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source str: ABCDEF Hello World !!! END zero (XYZ)
coder  str: PQRSTU Wtaad Ldgas !!! TCS otgd (MNO)
decode str: ABCDEF Hello World !!! END zero (XYZ)
https://ideone.com/rCZATY
language:
C (gcc 8.3)
created:
8 years ago
visibility:
public

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