fgets and clear input buffer not working in reading user inputs - c

Question

My program is fairly simple.
Read the H,W, horizontal char, vertical char from a user.
And then print out the square by the given params.
However, when user type 'y' to run the second time.
the height param is always missing.
I didn't get it.
A likely buggy point i can think is that the input buffer might not clean.
Any idea?
C program
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <memory.h>
const int USER_INPUT_SIZE_EACH_LINE = 999;
void draw_middle_lines(char *middle_line, int width) {
printf("%s", middle_line);
for (int i = 2; i < width; i++) {
printf(" ");
}
printf("%s\n", middle_line);
}
void draw_bound_line(char *bound_char, int width) {
for (int i = 0; i < width; i++) {
printf("%s", bound_char);
}
printf("\n");
}
void clearNewline(char *line, int max_len) {
for (int i = 0; i < max_len; i++){
printf("%c", line[i]);
}
printf("\n");
for (int i = 0; i < max_len; i++) {
if (line[i] == '\n') {
line[i] = '\0';
}
}
}
char **ask_user_preference() {
printf("\nask user preference\n");
const int NUM_OF_PROMPTS = 4;
const char *prompt[] = {
"please input height:",
"please input width:",
"please input horizontal char:",
"please input vertical char:",
};
char **preference;
preference = malloc(NUM_OF_PROMPTS);
for (int i = 0; i < NUM_OF_PROMPTS; i++) {
preference[i] = malloc(USER_INPUT_SIZE_EACH_LINE);
memset(preference[i], 0, sizeof(char) * USER_INPUT_SIZE_EACH_LINE);
printf("%s", prompt[i]);
fgets(preference[i], USER_INPUT_SIZE_EACH_LINE, stdin);
clearNewline(preference[i], USER_INPUT_SIZE_EACH_LINE);
}
return preference;
}
void draw(int w, int h, char *bound_char, char *middle_char) {
printf("width: %d\n", w);
printf("height: %d\n", h);
draw_bound_line(bound_char, w);
for (int i = 2; i < h; i++) {
draw_middle_lines(middle_char, w);
}
draw_bound_line(bound_char, w);
}
void clr_input_buffer() {
for (;;) {
int c = getchar();
if (c == EOF || c == '\n')
break;
}
}
int main() {
char *cont = malloc(10+1);
do {
char **pref = ask_user_preference();
int height = atoi(pref[0]);
int width = atoi(pref[1]);
char *bound_char = pref[2];
char *middle_char = pref[3];
draw(width, height, bound_char, middle_char);
printf("continue to play (y/n)? ");
fgets(cont, 2, stdin);
if (strncmp(cont, "y", 1) == 0) {
clr_input_buffer();
}else{
break;
}
} while (1);
printf("BYE BYE~");
return 0;
}