C得到未知的输入长度

Question

我的问题在另一个以前的旧问题中得到了回答，但只用代码回答，没有解释link。
我很想回答为什么那里的代码有效而我的无效（我错过了什么？），这是我的：

#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);
}

在答案代码中，他还写了+=16，这不是浪费内存吗？

Answer 1

它正在工作，谢谢“@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);
}