Language: C

#include <stdio.h>

int main(void)
{
  char s[1200];
  int cnt[26] = {0};
  int i;

  gets(s);

  for(i = 0; i < 1200; i++)
    switch(s[i]){
 case 'a' || 'A' : cnt[0]++;   break;
 case 'b' || 'B' : cnt[1]++;   break;
 case 'c' || 'C' : cnt[2]++;   break;
 case 'd' || 'D' : cnt[3]++;   break;
 case 'e' || 'E' : cnt[4]++;   break;
 case 'f' || 'F' : cnt[5]++;   break;
 case 'g' || 'G' : cnt[6]++;   break;
 case 'h' || 'H' : cnt[7]++;   break;
 case 'i' || 'I' : cnt[8]++;   break;
 case 'j' || 'J' : cnt[9]++;   break;
 case 'k' || 'K' : cnt[10]++;  break;
 case 'l' || 'L' : cnt[11]++;  break;
 case 'm' || 'M' : cnt[12]++;  break;
 case 'n' || 'N' : cnt[13]++;  break;
 case 'o' || 'O' : cnt[14]++;  break;
 case 'p' || 'P' : cnt[15]++;  break;
 case 'q' || 'Q' : cnt[16]++;  break;
 case 'r' || 'R' : cnt[17]++;  break;
 case 's' || 'S' : cnt[18]++;  break;
 case 't' || 'T' : cnt[19]++;  break;
 case 'u' || 'U' : cnt[20]++;  break;
 case 'v' || 'V' : cnt[21]++;  break;
 case 'w' || 'W' : cnt[22]++;  break;
 case 'x' || 'X' : cnt[23]++;  break;
 case 'y' || 'Y' : cnt[24]++;  break;
 case 'z' || 'Z' : cnt[25]++;  break;
  }
 

  for(i = 0; i < 26; i++)
    printf("%c : %d\n", 'a' + i, cnt[i]);

  return 0;
}

Compiler output:
main.c: In function 'main':
main.c:9:3: error: implicit declaration of function 'gets'; did you mean 'fgets'? [-Wimplicit-function-declaration]
    9 |   gets(s);
      |   ^~~~
      |   fgets
main.c:14:2: error: duplicate case value
   14 |  case 'b' || 'B' : cnt[1]++;   break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:15:2: error: duplicate case value
   15 |  case 'c' || 'C' : cnt[2]++;   break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:16:2: error: duplicate case value
   16 |  case 'd' || 'D' : cnt[3]++;   break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:17:2: error: duplicate case value
   17 |  case 'e' || 'E' : cnt[4]++;   break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:18:2: error: duplicate case value
   18 |  case 'f' || 'F' : cnt[5]++;   break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:19:2: error: duplicate case value
   19 |  case 'g' || 'G' : cnt[6]++;   break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:20:2: error: duplicate case value
   20 |  case 'h' || 'H' : cnt[7]++;   break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:21:2: error: duplicate case value
   21 |  case 'i' || 'I' : cnt[8]++;   break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:22:2: error: duplicate case value
   22 |  case 'j' || 'J' : cnt[9]++;   break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:23:2: error: duplicate case value
   23 |  case 'k' || 'K' : cnt[10]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:24:2: error: duplicate case value
   24 |  case 'l' || 'L' : cnt[11]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:25:2: error: duplicate case value
   25 |  case 'm' || 'M' : cnt[12]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:26:2: error: duplicate case value
   26 |  case 'n' || 'N' : cnt[13]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:27:2: error: duplicate case value
   27 |  case 'o' || 'O' : cnt[14]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:28:2: error: duplicate case value
   28 |  case 'p' || 'P' : cnt[15]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:29:2: error: duplicate case value
   29 |  case 'q' || 'Q' : cnt[16]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:30:2: error: duplicate case value
   30 |  case 'r' || 'R' : cnt[17]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:31:2: error: duplicate case value
   31 |  case 's' || 'S' : cnt[18]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:32:2: error: duplicate case value
   32 |  case 't' || 'T' : cnt[19]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:33:2: error: duplicate case value
   33 |  case 'u' || 'U' : cnt[20]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:34:2: error: duplicate case value
   34 |  case 'v' || 'V' : cnt[21]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:35:2: error: duplicate case value
   35 |  case 'w' || 'W' : cnt[22]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:36:2: error: duplicate case value
   36 |  case 'x' || 'X' : cnt[23]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:37:2: error: duplicate case value
   37 |  case 'y' || 'Y' : cnt[24]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~
main.c:38:2: error: duplicate case value
   38 |  case 'z' || 'Z' : cnt[25]++;  break;
      |  ^~~~
main.c:13:2: note: previously used here
   13 |  case 'a' || 'A' : cnt[0]++;   break;
      |  ^~~~