#include <stdio.h>
#include <string.h>
#include <assert.h>

//写第一题脑子瓦塔了，传进去指针忘了解引用，并且没有让指针进行后移操作
int mystrlen(char* arr) {
	assert(arr != NULL);
	int len = 0;
	while (*arr != '\0') {
		arr++;
		len++;
	}
	return len;
}

char* mystrcpy(char* dest, char* source) {
	assert(dest != NULL);
	assert(source != NULL);
	char* head = dest;
	while (*source != '\0') {
		*dest = *source;
		dest++;
		source++;
	}
	*dest = '\0';
	return head;
}

//memmove 可以处理内存重叠的问题
void* mymemmove(void* destination, const void* source, size_t num) {
	assert(destination != NULL);
	assert(source != NULL);
	void* ret = destination;
	//这里记住void*类型不能运算，判断地址的原因是防止没有赋值的元素被覆盖,即为解决内存重叠的问题
	//判断之后才能决定从前往后赋值还是从后往前
	if (destination<source || (char*)destination>(char*)source + num) {
		while ((long)num != 0) {
			(char*)destination = (char*)source;
			(char*)destination+=1;
			(char*)source += 1;
			num--;
		}
	}
	else {
		destination = (char*)destination + num - 1;
		source = (char*)source + num - 1;
		while ((long)num != 0) {
			*(char*)destination = *(char*)source;
			(char*)destination -= 1;
			(char*)source -= 1;
			num--;
		}
	}
	return ret;
}

void* mymemcpy(void* destination, const void* source, size_t num) {
	assert(destination != NULL);
	assert(source != NULL);
	void* ret = destination;
	for (size_t i = 0; i < num; i++) {
		((char*)destination)[i] = ((char*)source)[i];
	}
	return ret;
}

const char* mystrstr(const char* str1, const char* str2) {
	assert(str1 != NULL);
	assert(str2 != NULL);
	assert(*str1 != '\0');
	assert(*str2 != '\0');
	char* red = str1;
	while (*red != '\0') {
		char* s1 = red;
		char* s2 = str2;
		while(*s1 == *s2&&*s1!='\0'&&*s2!='\0') {
			//指向相同往后比较
			s1++;
			s2++;
		}
		//这里s1和s2判断顺序有讲究，如果先判断s1的话是不对的，如果找到了字符串，恰好s1s2都指向了反斜杠零
		//此时就应该返回正确的指针了如果先判断s1的话就会又red++此时就把正确的答案错过了
		if (*s2 == '\0') {
			return red;
		}
		////2.
		//else if (*s1 = '\0') {
		//	red++;
		//}
		////3.*s1!=*s2
		//else {
		//	red++;
		//}
		else {
			red++;
		}
	}
	return NULL;
}

char* mystrcat(char* dest, const char* src) {
	assert(dest != NULL);
	assert(src != NULL);
	char* p = dest;
	while (*dest != '\0') {
		dest++;
	}
	while (*src != '\0') {
		*dest = *src;
		dest++;
		src++;
	}
	
	return p;
}

int mystrcmp(const char* str1, const char* str2) {
	assert(str1!=NULL);
	assert(str2!=NULL);
	while (*str1 != '\0' && *str2 != '\0') {
		if (*str1 < *str2) {
			return -1;
		}
		else if (*str1 > *str2) {
			return 1;
		}
		else {
			str1++;
			str2++;
		}
	}
	if (*str1 < *str2) {
		return -1;
	}
	else if (*str1 > *str2) {
		return 1;
	}
	else {
		return 0;
	}
}
int main() {
	char arr[20] = "hello";
	char arr1[] = "abcdabcdehello";
	char* str = mystrcat(arr, arr1);
	printf("%s",str);
	return 0;
}