C++ strlen(), strcpy(), strcat() 함수 만들기

#include <iostream>
using namespace std;

int StrLen(const char* a)
{
	int count = 0;

	while (a[count] != NULL)
		count++;

	return count;
}

char* StrCpy(char* a, char* b)
{
	char* c = a;

	int i = 0;

	while (b[i] != NULL)
	{
		a[i] = b[i];
		i++;
	}

	a[i] = NULL;

	return c;
}

char* StrCat(char* a, char* b)
{
	char* c;
	int lenA = StrLen(a);

	int i = 0;
	while (b[i] != NULL)
	{
		a[lenA + i] = b[i];
		i++;
	}

	a[lenA + i] = NULL;

	return c;
}

int main()
{

}