结果对了为啥报错，说用了非法内存

#include<stdio.h>
#include<stdbool.h>
int main() {
	bool sym=1;
	char num[20],b;
	int i = 0;
	while ((b = getchar()) != '\n') {
		if (i == 0 && b == '-') {
			sym = false;
			continue;
		}
		num[i++] = b;
	}
	int t = 0;
	if (sym == false) printf("-");
	for (int j = i-1; j >= 0; j--) {
		if (num[j] - '0' > 0) {
			t++;
		}
		if (t == 0) continue;
		else {
			printf("%c", num[j]);
		}
	}
	return 0;
}