#include<iostream>

using namespace std;

char* Encode(char[]);

int GetStrLength(char[]);
void Swap(char* arr, int index1, int index2);
int main() {
	char input[] = { "TESTTEST" };

	char* result = Encode(input);

	for (int i = 0; i < GetStrLength(result); i++)
	{
		cout << result[i];
	}
}

char* Encode(char arr[]) {
	int arrLength = GetStrLength(arr);

	char* encodedArr = new char[(arrLength * 3) + 1];

	int encodedArrCounter = 0;

	for (int i = 0; i < arrLength; i++)
	{
		int currentAsciiCode = arr[i];
		while (currentAsciiCode != 0) {

			encodedArr[encodedArrCounter] = (currentAsciiCode % 10) + '0';;
			encodedArrCounter++;
			currentAsciiCode /= 10;
		}

		encodedArr[encodedArrCounter++] = '_';
	}

	for (int i = 0; i < arrLength; i += 3)
	{
		Swap(encodedArr, i, i + 1);
	}

	encodedArr[encodedArrCounter - 1] = '\0';

	return encodedArr;
}

void Swap(char* arr, int index1, int index2) {
	char temp = arr[index1];
	arr[index1] = arr[index2];
	arr[index2] = temp;
}

int GetStrLength(char arr[]) {
	int counter = 0;

	while (arr[counter] != '\0')
		counter++;

	return counter;
}