I am having a problem with my program getting stuck on waiting for input after using getchar(). I used a loop to clear the buffer and the same functionality appears four times in my program but only on two instances of this while loop it gets stuck and I cannot understand why.

In the two working instances, the only difference is the missing else if statement but when I remove it from the non-working instances, the problem is not solved and they are still stuck on waiting for a second ENTER.

If I enter anything else than 'y' or 'Y', I am getting the 'invalid input' message and then I am asked for an input again so this functionality works. However, when I enter 'y' or 'Y', followed by ENTER, a new line appears and nothing happens. If I enter invalid input again, I am getting the 'invalid input' message and with correct input, I still get a new line and nothing happens. Only after a second ENTER after a correct input the code continues as it should.

A non-working instance:

 printf("Play a game? (Y/N): ");
 while (!is_valid) {
 user_choice = getchar();
 char ch;
 while ((ch = getchar()) != '\n' && ch != EOF) {} // clear the buffer
 if (user_choice == 'y' || user_choice == 'Y') {
 is_valid = true;
 play_game();
 }
 else if (user_choice == 'n' || user_choice == 'N') break;
 else {
 printf("Invalid input. Try again.\n");
 }
 } 

A working instance:

 printf("Roll dice ('R')\n");
 while (!is_valid) {
 first_roll = getchar(); 
 char ch;
 while ((ch = getchar()) != '\n' && ch != EOF) {} // clear the buffer
 if (first_roll == 'r' || first_roll == 'R') {
 is_valid = true;
 }
 else {
 printf("Invalid input. Try again.\n");
 }
 } 

Full code:

#include <stdio.h>
#include <stdbool.h> 
#include <stdlib.h> // For rand()
/*
2025年02月19日
RULES
Come-Out Roll:
You roll two dice.
 - If the sum is 7 or 11, you win right away.
 - If the sum is 2, 3, or 12 (called "craps"), you lose immediately.
 - If the sum is 4, 5, 6, 8, 9, or 10, that number becomes your point.
Point Phase:
Once a point is set, you keep rolling the dice.
 - If you roll the point number again before rolling a 7, you win.
 - If you roll a 7 before the point, you lose.
*/
int roll_dice(void);
bool play_game(void);
int main() {
 int roll = 0;
 char user_choice;
 bool is_valid = false;
 // Game loop
 printf("Play a game? (Y/N): ");
 while (!is_valid) { // In this loop it waits for a second ENTER
 user_choice = getchar();
 char ch;
 while ((ch = getchar()) != '\n' && ch != EOF) {} // clear the buffer
 if (user_choice == 'y' || user_choice == 'Y') {
 is_valid = true;
 play_game();
 }
 else if (user_choice == 'n' || user_choice == 'N') break;
 else {
 printf("Invalid input. Try again.\n");
 }
 } 
 
 return 0;
}
int roll_dice(void) {
 // Generate 2 random numbers 1-6
 int dices = (rand() % 12 + 1);
 // Sum the numbers
 return dices;
}
bool play_game(void) {
 bool result = false;
 bool is_valid = false;
 bool game_has_ended = false;
 char first_roll;
 char user_choice;
 int roll_result;
 
 getchar();
 // One dice roll
 printf("Roll dice ('R')\n");
 while (!is_valid) { // This loop goes fine
 first_roll = getchar(); 
 char ch;
 while ((ch = getchar()) != '\n' && ch != EOF) {} // clear the buffer
 if (first_roll == 'r' || first_roll == 'R') {
 is_valid = true;
 }
 else {
 printf("Invalid input. Try again.\n");
 }
 } 
 roll_result = roll_dice();
 int roll = 1;
 int point = 0;
 // Evaluate roll
 if (roll == 1)
 {
 switch (roll_result) {
 // Immediate win
 case 7: {
 result = true;
 point = 0;
 break;
 };
 case 11: {
 result = true;
 point = 0;
 break;
 };
 // Immediate lose
 case 2: {
 result = false;
 break;
 };
 case 3: {
 result = false;
 break;
 };
 case 12: {
 result = false;
 break;
 };
 // Point
 case 4: {
 roll = 2;
 point = 4;
 result = true;
 break;
 };
 case 5: {
 roll = 2;
 point = 5;
 result = true;
 break;
 };
 case 6: {
 roll = 2;
 point = 6;
 result = true;
 break;
 };
 case 8: {
 roll = 2;
 point = 8;
 result = true;
 break;
 };
 case 9: {
 roll = 2;
 point = 9;
 result = true;
 break;
 };
 case 10: {
 roll = 2;
 point = 10;
 result = true;
 break;
 };
 }
 }
 // Roll 1 results
 if (result == false) {
 printf("Roll 1: %d\n", roll_result);
 printf("You lose!\n");
 game_has_ended = true;
 }
 else if (result == true && roll == 1 && point == 0) {
 printf("Roll 1: %d\n", roll_result);
 printf("You win!\n");
 game_has_ended = true;
 }
 else {
 // Roll 2
 if (roll == 2 && point > 0) {
 printf("Point: %d\n", roll_result);
 char roll_2;
 bool is_valid = false;
 while (!is_valid) { // This loop goes fine
 printf("Press 'R' to roll again.\n");
 roll_2 = getchar(); 
 char ch;
 while ((ch = getchar()) != '\n' && ch != EOF) {} 
 if (roll_2 == 'r' || roll_2 == 'R') {
 is_valid = true;
 }
 else {
 printf("Invalid input. Try again.\n");
 }
 } 
 
 // Roll 2 results
 switch (roll_dice()) {
 case 7: {
 result = false;
 printf("Roll 2: %d\n", roll_dice());
 printf("You lose!\n");
 game_has_ended = true;
 break;
 }
 default: {
 result = true;
 printf("Roll 2: %d\n", roll_dice());
 printf("You win!\n");
 game_has_ended = true;
 break;
 }
 }
 }
 }
 // Recursion
 is_valid = false;
 printf("Play another game? (Y/N): ");
 while (!is_valid) { // In this loop it waits for a second ENTER
 user_choice = getchar();
 char ch;
 while ((ch = getchar()) != '\n' && ch != EOF) {} 
 if (user_choice == 'y' || user_choice == 'Y') {
 is_valid = true;
 play_game();
 }
 else if (user_choice == 'n' || user_choice == 'N') return game_has_ended;
 else {
 printf("Invalid input. Try again.\n");
 }
 }
 return game_has_ended;
}

Can you give me a hint of what I am doing wrong?