text: 
  #include <stdbool.h>
  #include <string.h>
  
  /*
      is_isogram: returns true if the given string a isogram, otherwise false.
  */
  bool is_isogram(const char phrase[]) 
  {
  
      /* use 'unsigned' because of the function strlen(...) */
      unsigned int i = 0;
      unsigned int j = 0;
  
      /* the current read character in the first for-loop */
      char current_char = ' ';
  
      /* return status */
      bool status = true;
  
      /* contains the length of the given string */
      unsigned int len_phrase = strlen(phrase);
  
      for (i = 0; i < len_phrase; i++ ) 
      {
          current_char = phrase[i];
  
          /* makes sure the current character has no repetition */
          for (j = i+1; j < len_phrase; j++)
          {
              if (current_char == phrase[j])
              {
                  status = false;
  
                  /* 
                      because the given string is none isogram.
                      that means we can exit the nested for-loop.
                  */
                  goto end;
              }
          }
      }
  
      /* exit label */
      end:
          return status;
  }
  