text: #define _USE_MATH_DEFINES
  
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  
  int main(void) {
    char text[300] = "hello  a b c - / d";
    int counter[26] = {0};
    for (int i = 0; i < strlen(text); i++) {
      if (text[i] >= 'A' && text[i] <= 'Z') {  // uppercase
        counter[text[i] - 'A']++;
      } else if (text[i] >= 'a' && text[i] <= 'z') {  // lowercase
        counter[text[i] - 'a']++;
      }
    }
    printf("%s %12s \n", "Letter", "Occurences");
  
    for (int i = 0; i < 26; i++) {
      printf("%c %c %12i \n", 'a' + i, 'A' + i, counter[i]);
    }
    return EXIT_SUCCESS;
  }
  