Check a race track

[Anlity]

So our teacher gave us the task to wirte a programm which checks for a given input if a race track can be completed.

The chars used are "/" for going uphill which slows the car by 1, "\" for going downhill, speeding the car up by 1 and "_" for a plain in which the driver has to decide whether he speeds up or slows down. The goal ist to complete a given track, having a speed of 0 at the end.

\\/__/ -> possible
\\/__ -> not possible

The speed of the car can be 0 during the race, if the following char is a "\" or a "_".

The drivers can now walk along the track and evaluate whether they'll manage to finish it with a speed of 0 or not. Limitations are that I can read through the parcour exactly once, and may not "jump" from one part of the string to another, as well as using the least possible amount of memory, as the drivers are bad at memorizing things.

So far my code looks like this, but I think I violated one of the limitations, as I check what parcourPart[i + 1] looks like...
Does anybody have an idea how to solve this problem?

#include <iostream>
#include <fstream>
#include <string>
#include<vector>
#include <stdlib.h>

bool check(std::string parcour);
int evaluatePart(std::string parcourPart, int currSpeed);

int main(int argc, char** argv)
{
	std::string line, parcour;
	std::ifstream myfile("parcourstest.txt");//argv[1]);
	bool canFinish = false;
	

	if (myfile.is_open())
	{
		while (std::getline(myfile, line))
		{
			parcour += line;
		}

		myfile.close();
	}
	else std::cout << "Unable to open file";
	parcour += "#";
	if (parcour.size() < 102) {
		std::cout << parcour;
	}

	canFinish = check(parcour);
	if (canFinish) {
		std::cout << "\b I can do that!";
	}
	else std::cout << "\b No way!";

    return 0;
}

bool check(std::string parcour) {
	int i = 0, speed = 0;
	std::string part = "";

	while (parcour[i] != '#')
	{
		part += parcour[i];

		if (part.size() == 5 || parcour[i+1]=='#') {
			if (evaluatePart(part, speed) > -1) {
				speed = evaluatePart(part, speed);
			}
			else return false;
			
			part.clear();
		}
		i++;
	}
	if (speed > 0 || speed < 0) {
		return false;
	}
	else
	{
		return true;
	}
	
}

int evaluatePart(std::string parcourPart, int currSpeed) {
	
	for (int i = 0; i < parcourPart.size(); i++)
	{
		if (parcourPart[i] == '\\') {
			currSpeed += 1;
		}
		else if (parcourPart[i] == '/' && currSpeed != 0)
		{
			currSpeed -= 1;
		}
		else if (parcourPart[i] == '/' && currSpeed == 0)
		{
			return -1;
		}
		else if (parcourPart[i] == '_')
		{
			if (currSpeed > 0 && parcourPart[i+1] != '/') {
				currSpeed -= 1;
			}
			else {
				currSpeed += 1;
			}
		}
	}
	return currSpeed;
}

[Anlity]

Nobody? I just need another way to solve this problem.

[lastchance]

You must store two levels in order to do the comparison. However, as far as deciding whether the zero speed is legitimate or not, why don't you store lastSpeed?

If lastSpeed is/was 0 then you fail if the present (level i) is NOT a "\" or a "_".

[Anlity]

You must store two levels in order to do the comparison.

I'm sorry that I might have explained it wrong, I don't have to compare two tracks, I just need to check whether a given track is ok.

If lastSpeed is/was 0 then you fail if the present (level i) is NOT a "\" or a "_".

Yeah, but the problem is the part where the programm decides what to do on a plain part of the track.

else if (parcourPart[i] == '_')
		{
			if (currSpeed > 0 && parcourPart[i+1] != '/') { 
				currSpeed -= 1;
			}
			else {
				currSpeed += 1;
			}
		}

I'm not sure what you mean with lastSpeed. At the moment I'm updating currSpeed and using this as the speed at the time the driver passes a certain part of the track. Where should I use lastSpeed?

As an example:

\ _ _ /
1 0 1 0 

This is what my programm calculates at the moment. As it goes through the programm like this:

 //first step:
for (int i = 0; i < 4; i++) //currSpeed is 0, parcourPart[0] is \\
	{
		if (parcourPart[0] == '\\') { //this is the first char
			currSpeed += 1; //-> currSpeed = 1;
		}
		else if (parcourPart[0] == '/' && currSpeed != 0)
		{
			currSpeed -= 1;
		}
		else if (parcourPart[0] == '/' && currSpeed == 0)
		{
			return -1;
		}
		else if (parcourPart[0] == '_')
		{
			if (currSpeed > 0 && parcourPart[0+1] != '/') {
				currSpeed -= 1;
			}
			else {
				currSpeed += 1;
			}
		}
	}
	return currSpeed;

 //second step:
for (int i = 0; i < 4; i++) //currSpeed is 1, parcourPart[1] is _
	{
		if (parcourPart[1] == '\\') {
			currSpeed += 1;
		}
		else if (parcourPart[1] == '/' && currSpeed != 0)
		{
			currSpeed -= 1;
		}
		else if (parcourPart[1] == '/' && currSpeed == 0)
		{
			return -1;
		}
		else if (parcourPart[1] == '_')
		{
			if (currSpeed > 0 && parcourPart[1+1] != '/') { //currSpeed == 1,parcourPart[2] == _
				currSpeed -= 1; //-> currSpeed = 0 
//BUT here I checked parcourPart[2] before being finished with parcourPart[1] which is my problem.
			}
			else {
				currSpeed += 1;
			}
		}
	}
	return currSpeed;

What would I change if I implemented lastSpeed?