Problem understanding rand()

[Serri]

So i'm doing some of the beginner exercises that was posted on this website

http://www.cplusplus.com/forum/articles/12974/ 

namely the "bracket search" i'm on the 4 star challenge and i'm having some problems :<

challenge:

Pick a number and have the program guess it. modify the program so that no matter what number the user thinks of (1-100) the computer can guess it in 7 or less guesses.

What i'm having problem with is getting rand() to do what i want. I want it to search in a specific range.

I understand it very basic like for example if i were to write

rand()% 100 + 1;

this would generate a number within the range 1-100 the problem occurs when i try to have ranges like from 40-50

i know the code for it would be rand()% 10 + 40;

But i don't understand how i can get the program to update the specific range by itself.

so for example it would be like this

user has a number between 1-100 let's say he picks 19

the program generates the number 29

this number is higher than the what the user inputed

so the program should now search 1-29

the program generates 15

this number is lower than the one the user picked

so the program now searches 15-29

and so on til the program finds the correct number. but i have no idea how to do this, could anyone help? :>

i've done most of the code as i said it's the rand() part giving me trouble

[Disch]

I think the point is to make the computer 'divide and conquer' to determine the number the user picked. In which case you shouldn't be using rand at all.

[Serri]

is it not divide and conquer to eliminate all wrong choices and all that is left with is the correct choice?

anyways here's the whole code, got it working after a few hours :>

#include <iostream>
#include <Windows.h>
#include <string>
#include <time.h>

int RandomNumber, Number, Tries, SecretNumber, HighValue ,LowValue,range;
std::string Answer;


int main()
{
	
	std::cout << "Enter a secret number" << std::endl;
	std::cin >> SecretNumber;
	system("CLS");
	srand ( time(NULL) );
	HighValue = 100;
	LowValue = 1;
	RandomNumber = rand() % HighValue + LowValue;

	while(Tries <=7)
	{
		Tries++;

	std::cout << RandomNumber << " is this your number? please tell me if it's higher or lower then your number" << std::endl;
	std::cin >> Answer;
	std::cout << "" << std::endl;
	
	if(Answer ==  "higher")

	{
		
		RandomNumber--;
		HighValue = RandomNumber;
		range =(HighValue-LowValue)+1;

		RandomNumber = LowValue+int(range*rand()/(RAND_MAX+1.0));
	
		
	}
		else if(Answer ==  "lower")
	{


		RandomNumber++;
		LowValue = RandomNumber;
	    range =(HighValue-LowValue)+1;
		RandomNumber = LowValue+int(range*rand()/(RAND_MAX+1.0));

	}



		else if(Answer ==  "correct")
	{
	std::cout <<"yay" << std::endl;
	system("pause");
	return 0;
	}




	}
	
	
	
}

[Moschops]

modify the program so that no matter what number the user thinks of (1-100) the computer can guess it in 7 or less guesses.

There's no guarantee of this by randomly picking values within the possible range. It could take 100 guesses.

[Serri]

well crap :> forgot to think about how that :<

[Disch]

Divide and conquer is to choose numbers to eliminate the maximum number of possibilities. In a situation like this one, it means cutting the possibilities in half.

Example number: 48

guess 1) 50 (lower)
guess 2) 25 (higher)
guess 3) 37 (higher)
guess 4) 43 (higher)
guess 5) 46 (higher)
guess 6) 48 (correct!)

[Serri]

that's what i thought of aswell Disch. however is their any otherway to do this than to do have a ton of if statements?`?

[DesiredNote]

I have an idea in mind, and will make this tonight. I'll post here with my solution.

[whitenite1]

@Serri

You don't need a ton of if's. Just the one's you already have. I removed the 'else' part, cause I felt they weren't really necessary. Also added in a section that checks if you cheated at the end. Removed the System("CLS") call, as a lot of programmers frown on it. Anyway, here's the newer version.

// Computer Guess Number.cpp : main project file.

#include "stdafx.h"
#include <iostream>
#include <Windows.h>
#include <string>
#include <ctime>

void ClearScreen();

int RandomNumber, Number, Tries=0, SecretNumber, HighValue ,LowValue,range;
char Answer;

int main()
{

	std::cout << "Enter a secret number" << std::endl;
	std::cin >> SecretNumber;
	time_t t;
	srand((unsigned) time(&t));
	HighValue = 100;
	LowValue = 1;

	RandomNumber = rand() % 100;

	do
	{
		ClearScreen();
		std::cout << "Is " << RandomNumber << " 'H'igher or 'L'ower than your number? Or am I 'C'orrect?" << std::endl;
		Tries++;
		std::cin >> Answer;
		Answer = tolower(Answer);
		std::cout << std::endl;

		if(Answer ==  'h')
		{
			HighValue = RandomNumber-1;
			range =(HighValue-LowValue)/2;
			RandomNumber = range+LowValue;
		}
		if(Answer ==  'l')
		{
			LowValue = RandomNumber+1;
			range =(HighValue-LowValue)/2;
			RandomNumber = range+LowValue;
		}
		if(Answer ==  'c')
		{
			std::cout <<"Yay. I got in " << Tries << " guesses.." << std::endl;
			system("pause"); // There are better alternatives. Left it here for now.
			return 0;
		}
	} while(Tries < 7);

	std::cout <<"I used all of my " << Tries << " guesses.." << std::endl;
	std::cout << "You win this time. Now I'll peek at your number.." << std::endl;
	Sleep(2000);
	std::cout << "I see you picked " << SecretNumber << " as your secret number." << std::endl;
	if ( SecretNumber < LowValue || SecretNumber > HighValue)
		std::cout << "I also see that you could only beat me by CHEATING!! SHAME ON YOU!!" << std::endl;
	return 0;
}

void ClearScreen()
{
	DWORD n;
	DWORD size;
	COORD coord = {0};
	CONSOLE_SCREEN_BUFFER_INFO csbi;
	HANDLE h = GetStdHandle ( STD_OUTPUT_HANDLE );
	GetConsoleScreenBufferInfo ( h, &csbi );
	size = csbi.dwSize.X * csbi.dwSize.Y;
	FillConsoleOutputCharacter ( h, TEXT ( ' ' ), size, coord, &n );
	GetConsoleScreenBufferInfo ( h, &csbi );
	FillConsoleOutputAttribute ( h, csbi.wAttributes, size, coord, &n );
	SetConsoleCursorPosition ( h, coord );
}