Initialize variable

[thinhphucvang]

I have a code like this from cprogramming.com, I don't understand why "guess" has to be -1. How about initialize it 0?

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;
int main()
{
	srand(time(NULL));
	int num = rand() % 100;
	int guess = -1;
	int trycount = 0;
	while (guess != num && trycount < 8)
	{
		cout << "Enter your guess: ";
		cin >> guess;
		if (guess < num)
		{
			cout << "Wrong! You entered the smaller number! Try again!\n";
		}
		if (guess > num)
		{
			cout << "Wrong! You enter a higher number! Try again!\n";
		}
		trycount++;
	}
	if (guess == num)
	{
		cout << "You're right! Woo hoo! Hello smart guy! :)\n";
	}
	else
	{
		cout << "You fool! The number is " << num << endl;
	}	
}

[JLBorges]

> How about initialize it 0?

num (rand() % 100) may be equal to zero.

Somewhat more compact:

#include <iostream>
#include <cstdlib>
#include <ctime>

int main()
{
	std::srand( std::time(nullptr) );

	const int num = std::rand() % 100 ;
	int guess ;

	for( int trycount = 0 ;
	     std::cout << "Enter your guess: " && std::cin >> guess && guess != num && trycount < 8 ;
	     ++trycount )
	{
		if (guess < num) std::cout << "Wrong! You entered the smaller number! Try again!\n";
		else std::cout << "Wrong! You enter a higher number! Try again!\n";
	}

	if (guess == num) std::cout << "You're right! Woo hoo! Hello smart guy! :)\n";
	else std::cout << "You fool! The number is " << num << '\n' ;
}

[thinhphucvang]

Why does num(rand % 100 ) can be 0? Sorry, I just don't get it clearly!

[JLBorges]

n%100 == 0 if n is an integral multiple of 100

0%100 == 0, 100%100 == 0, 200%100 == 0 etc.

[thinhphucvang]

God! How about 2?

[JLBorges]

See: http://www.cprogramming.com/tutorial/modulus.html

Try this out:

#include <iostream>

int main()
{
   for( int n : { 0, 2, 100, 700, 567, 1789 } )
   {
       std::cout << n << " % 100  ==  " << n % 100 << '\n'
                 << -n << " % 100  ==  " << -n % 100 << '\n'
                 << n << " % -100  ==  " << n % -100 << '\n'
                 << -n << " % -100  ==  " << -n % -100 << "\n\n" ;
   }
}

[thinhphucvang]

Thank you!