int my_strlen(const char* p) {
	int size = 0;
	//找到末尾停止
	while (*p != '\0') {
		p++;
		size++;
	}
	return size;
}

char* my_strcpy(char* dest, const char* src) {

	//判斷傳入是否為空
	if (src == NULL || dest == NULL) {
		return dest;
	}
	char* pdest = dest;
	//不為空打印
	while (*src != '\0') {
		*pdest = *src;
		pdest++;
		src++;
	}
	//末尾加'\0'
	*pdest = '\0';
	return dest;

}

int my_strcmp(const char* str1, const char* str2) {
	//一直往后查找直到其中一個結(jié)尾或者他們二者不相等為止
	while (*str1 != '\0' && *str2 != '\0' && (*str1 == *str2)) {
		str1++;
		str2++;
	}
	return *str1 - *str2;
}

char* my_strcat(char* dest, const char* src) {

	char* pdest = dest;
	//pdset先走到末尾
	while (*pdest != '\0') {
		pdest++;
	}
	//鏈接
	while (*src != '\0') {
		*pdest = *src;
		pdest++;
		src++;
	}
	//加結(jié)尾標志'\0'
	*pdest = '\0';
	return dest;
}

char* my_strstr(const char* dest, const char* src) {

	//斷言非空
	assert(dest && src);

	while (*dest != '\0') {
		//記錄dest src初始位置
		char* pdest = dest;
		char* psrc = src;
		//若相等則繼續(xù)比較
		while (*pdest == *psrc || *psrc == '\0') {
			//如果psrc=='\0' 則說明找到子串
			if (*psrc == '\0') {
				return dest;
			}
			//psrc 未到 \0 則繼續(xù)比較是否相等
			pdest++;
			psrc++;
		}
		dest++;
	}
	return NULL;
}