check the validation of the guessed letter

src/main/c/Hangman/playHangman.c

@@ -14,9 +14,21 @@ void playHangman(char *wordToGuess) {
 
         // Get a letter from the player
         char guess;
-        printf("\n\t Enter your guess (lower case): ");
+        printf("Enter your guess: \n");
         scanf(" %c", &guess);
 
+        // check if the guess is lower case and is a letter (valid)
+        if (!isalpha(guess) || isupper(guess)) {
+            printf("Please enter a valid lowercase alphabet.\n");
+            continue;
+        }
+
+        // Check if the letter has already been guessed by the player
+        if (strchr(guessedLetters, guess) != NULL) {
+            printf("You already guessed that letter. Try another letter.\n");
+            continue;
+        }
+
         // Add the guessed letter to the list
         guessedLetters[strlen(guessedLetters)] = guess;