Why is reallocation in my program not working properly? - c

Question

I want to make a program that stores inputed words into a 2D array (it can be as many as you want) and once you input word 'END', program should get out of the while loop. But for now user can input max. 5 words, and once he do that, program should reallocate 2d array with more rows. But there's something wrong with reallocation and I dont know what.
Here's a code:
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX 20
char** allocate(int n, int m) {
char** arr = (char**)malloc(sizeof(char*) * n);
for (int i = 0; i < n; i++)
arr[i] = (char*)malloc(sizeof(char) * m);
return arr;
}
void printList(char** polje, int n, int m) {
for (int i = 0; i < n; i++) {
printf("%s\n", polje[i]);
}
}
int main() {
int n = 5;
int index = 0;
char** list = allocate(5,MAX);
char input[MAX];
while (strcmp("END", input)) {
scanf(" %s", input);
if (index % 5 == 0) {
n += 5;
list = (char**)realloc(list, sizeof(char*) * n);
for (int i = 0; i < n; i++)
list[i] = (char*)realloc(list[i], sizeof(char) * MAX);
}
if (strcmp("END", input) != 0) {
strcpy(list[index], input);
index++;
}
}
printList(list, index, MAX);
return 0;
}

Answer 1

The problem is that realloc is being called with an invalid pointer.
After:
n += 5;
list = (char**)realloc(list, sizeof(char*) * n);
list[n - 5], list[n - 4], list[n - 3], list[n - 2], and list[n - 1] contain invalid pointer values. So in the subsequent:
for (int i = 0; i < n; i++)
list[i] = (char*)realloc(list[i], sizeof(char) * MAX);
The realloc is being passed invalid pointers when i is in the range n - 5 to n - 1.