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  1. #include <stdio.h>
  2.  
  3. int isalphabet(char c) {
  4.     return (('A' <= c && c <= 'Z') || ('a' <= c && c <= 'z'));
  5. }
  6.  
  7. char caesar(char c, int n) {
  8.     if (!isalphabet(c)) return c;
  9.     char base = ('A' <= c && c <= 'Z') ? 'A' : 'a';
  10.     int pos = c - base;
  11.     pos = (pos + n + 26) % 26;
  12.     return base + pos;
  13. }
  14.  
  15. int main() {
  16.     char str[100];
  17.     int n;
  18.  
  19.     printf("文字列を入力: ");
  20.     fgets(str, sizeof(str), stdin);
  21.  
  22.     printf("シフト数nを入力: ");
  23.     scanf("%d", &n);
  24.  
  25.     printf("暗号化結果: ");
  26.     for (int i = 0; str[i] != '\0'; i++) {
  27.         printf("%c", caesar(str[i], n));
  28.     }
  29.  
  30.     printf("\n復号結果: ");
  31.     for (int i = 0; str[i] != '\0'; i++) {
  32.         printf("%c", caesar(str[i], -n));
  33.     }
  34.  
  35.     printf("\n");
  36.     return 0;
  37. }
Success #stdin #stdout 0s 5312KB
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Standard input is empty
stdout
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文字列を入力: シフト数nを入力: 暗号化結果: 
復号結果:
https://ideone.com/kWhnN7
language:
C (gcc 8.3)
created:
8 hours ago
visibility:
public

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