Question about if statement and loop

[Violet_82]

Hi guys, I have just written 2 versions of this simple program:

#include <iostream>
using std::cin;
using std::cout;

int main ()
{
cout << "This program counts from 10 to 0. \nGuess the missing number.\n";
int n;
int f;
for (n=10; n>0; n--)
	{
	if (n==5) continue;
	cout << n << ", ";
	}
cout << "So, type the missing number here: ";
cin >>f;
	if (f==5)
	cout << "Well done!\a\a\a";
	while (f!=5)
	{
	cout << "Wrong answer, try again!\nEnter the number here: ";
	cin >> f;
	}
	
return 0;
}

I compiled it and executed it but it doesn' work properly: if I guess the number on the first attempt, all good, but, say that at the first attempt I try with 4 (and the program will obviously say tht that's wrong asking me to try again) and then I type 5, the program terminates, without showing me "Well done" and ringing the system alarm three times.
Now in the second version I changed the order of the if statement and the while loop so that line 17 and 18 come after the while loop:

#include <iostream>
using std::cin;
using std::cout;

int main ()
{
cout << "This program counts from 10 to 0. \nGuess the missing number.\n";
int n;
int f;
for (n=10; n>0; n--)
	{
	if (n==5) continue;
	cout << n << ", ";
	}
cout << "So, type the missing number here: ";
cin >>f;
	
	while (f!=5)
	{
	cout << "Wrong answer, try again!\nEnter the number here: ";
	cin >> f;
	}
	if (f==5)
	cout << "Well done!\a\a\a";
return 0;
}

Now, this one here works fine. What I would like you guys to help me with, is to understand why.
thanks

[ajsavoca]

The problem is that while loop. When f is not 5, that sequence will continue to loop but as soon as f equals 5 then it will continue on to the next line which is not the "well done".

[Violet_82]

Hi there,
thanks for that. uhm, I thought the next line was the "well done" bit because I have the loop and then the if statement so, if f is not 5 the loop will execute, if f is 5 then the loop won't execute and it will jump straight to the "well done" line. Is it not like that?
thanks

[WaltP]

cout << "So, type the missing number here: ";
cin >>f;
	if (f==5)
	cout << "Well done!\a\a\a";
	while (f!=5)
	{
	cout << "Wrong answer, try again!\nEnter the number here: ";
	cin >> f;
	}
    return 0;
}

Look more closely at this piece of code. If you enter 5, as you say it works fine. But if you enter 4 the first thing the code does is:

cout << "So, type the missing number here: ";
cin >>f;
	if (f==5)
	cout << "Well done!\a\a\a";

Nothing prints because f != 5
Then the program continues and executes this code:

while (f!=5)
	{
	cout << "Wrong answer, try again!\nEnter the number here: ";
	cin >> f;
	}
    return 0;
}

You enter the loop and keep asking for another number until f==5
What happens when you exit the loop? What's missing?

[MyrtleTurtle]

It is because each line executes in order. The order you have here is to check if f == 5 first, and if so then cout<< your message. If f!=5 though, it will check to see if f==5 once, then go into the loop. There is no code to take you back to the check to see if f==5 and cout<< your message after you exit the loop (when f==5).

if (f==5)	cout << "Well done!\a\a\a";	while (f!=5)	{	cout << "Wrong answer, try again!\nEnter the number here: ";	cin >> f;	}

This one keeps asking for input as long as f!=5. Then, whenever f==5, it will exit the loop and go on to your if statement to check the value of f.

cin >>f;
	
	while (f!=5)
	{
	cout << "Wrong answer, try again!\nEnter the number here: ";
	cin >> f;
	}
	if (f==5)
	cout << "Well done!\a\a\a";

edit: Oops, Walt, you beat me to it. I finally found a question I can answer...so I'll leave my answer here even though it's the same thing you said.

[Violet_82]

ok, so fondamentally, what you guys are saying is that the if statement has to be after the loop, whic makes sense, because we need to tell exit the loop if f=5.
I presume this thing of having the f statement after the loop is always valid when they are used together

[MyrtleTurtle]

Yes, depending on what you want to do. But in this case you really don't even need the if statement, since the loop will only stop whenever f==5. So we already know that it's 5, and don't need to check.

I would think that this logic is always valid whenever you have a while loop that ends when a certain value is reached and then you want to check for that value after exiting the loop.

But if you want to check for a certain value before entering the while loop, then you'd put the if statement first.

[Violet_82]

Ok so I can simply remove the line that goes

#
if (f==5)

and nothing at all will change.
Let me get to this though:

But if you want to check for a certain value before entering the while loop, then you'd put the if statement first.

Any chance you can give me a practical simple example?Just so I understand it properly
thanks