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

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