C getting unknown input length - c

Question

My question was answered in another previous old question here but it was answered with code only & no explanation link.
I would love an answer why the code there works & mine not (what I'm missing?), this is mine:
#include <stdio.h>
#include <stdlib.h>
void get_sentence(char* sentence) {
char end_of_input = 'a', * temp_pointer = NULL;
for (unsigned short int input_index = 0; end_of_input != '\n'; input_index -= -1) {
temp_pointer = sentence;
sentence[input_index] = end_of_input = getchar();
printf("%d: %c\n", (1 + input_index), end_of_input);
if (end_of_input == '\n') {
printf("end of input\n");
sentence[input_index] = '\0';
return;
}
sentence = (char*)realloc(sentence, ((int)(input_index + 2)) * sizeof(char));
if (sentence == NULL) {
free(temp_pointer);
return;
}
}
}
void main(int argc, char const* argv[]) {
char* sentence = malloc(sizeof(char));
if (sentence == NULL) {
printf("blyat");
exit(1);
}
get_sentence(sentence);
printf("Answer = ");
for (unsigned short int run = 0; sentence[run] != '\0'; run -= -1)
printf("%c", sentence[run]);
printf("\n");
free(sentence);
exit(0);
}
In the answer code he also does +=16 which is a waste of memory isn't it?.

Answer 1

IT IS WORKING THANK YOU "#Johnny Mopp" ♥.
#include <stdio.h>
#include <stdlib.h>
char* get_sentence() {
char end_of_input = 'a', *sentence = malloc(sizeof(char)), *temp_pointer = NULL;
for (unsigned short int input_index = 0; end_of_input != '\n'; input_index -= -1) {
temp_pointer = sentence;
sentence[input_index] = end_of_input = getchar();
if (end_of_input == '\n') {
sentence[input_index] = '\0';
return sentence;
}
sentence = (char*)realloc(sentence, ((int)(input_index + 2)) * sizeof(char));
if (sentence == NULL) {
free(temp_pointer);
return NULL;
}
}
}
int main(int argc, char const* argv[]) {
char* sentence = get_sentence(&sentence);
if (!sentence)
exit(1);
printf("Answer: %s\n", sentence);
free(sentence);
exit(0);
}