下载数据测了一下，跟题解答案一毛一样，就是过不了...求助大佬

#include <stdio.h>
#include <string.h>
char a[1000] = { '\0' }, str[100] = { 0 };
int main()
{
	int n, c1, c2;
	int num;
	scanf("%d", &n);
	scanf("%s", a);
	for (int i = 0; i < n; i++)
	{
		scanf("%d", &num);
		if (num == 1)
		{
			scanf("%s", str);
			strcat(a, str);
			printf("%s\n", a);
		}
		else if (num == 2)
		{
			scanf("%d %d", &c1, &c2);
			a[c1 + c2] = '\0';
			strcpy(str, &a[c1]);
			strcpy(a, str);
			printf("%s\n", a);
		}
		else if (num == 3)
		{
			scanf("%d", &c1);
			scanf("%s", str);
			strcat(str, &a[c1]);
			a[c1] == '\0';
			strcat(a, str);
			printf("%s\n", a);
		}
		else if (num == 4)
		{
			scanf("%s", str);
			char *m = strstr(a, str);
			if (m != NULL)
				printf("%d\n", (int)(m - a));
			else
				printf("%d\n", -1);
		}
	}
	return 0;
}