Setting ints

[Veight]

I am currently re-learning everything about coding. (haven't done it in 3 years)
Anyways, as I am working on problem 2 @ projecteuler.net I am having a problem that I know has a quick fix. I am having a problem with these two lines.

prev2 = prev1;
prev1 = i;

Both are declared but i'm getting the "left operand must be l-value"

[R0mai]

How are prev1 and prev2 declared?

[Veight]

int prev1 = 2;
int prev2 = 1;

[R0mai]

There are no problems with this. Could you post a small compilable code which produces this error for you?

[Veight]

Er, I just realized the lines were off. I figured it out. Thanks anyways. Hehe.

[Blessman11]

have you declared i, I think it may be getting confused

[R0mai]

if (prev1 + prev2 = i) This line is what produces the error. Did you mean ==?
Original got deleted.

EDIT: 500th post

[Veight]

Alright. I thought I figured it out but I am still having a problem.

	int i = 0;
	int answer = 0;
	int prev1 = 2;
	int prev2 = 1;
	for(i = 0; i<=4000000; i++)
	{
		if (i = prev1 + prev2)
		{
			prev1 = prev2;
			i = prev1;
			if(i%2 = 0)
			{
				answer += i;
			}
		}

Getting an error at the second if loop

[R0mai]

= is the assignment operator. You meant == which is the equality operator.

[Blessman11]

what do you mean by answer += i, is += only used for comparisons.
please explain to me if += has other uses unrelated to comparisons since I don't know any

[Veight]

What I was having it do was add up all of the even numbers. More problems in this than I originally though. Heh.

[Blessman11]

R0mai guy is write, when comparing its ==, and when assigning a value its =

if expressions can't be initialised to assign values, I don't know whether I've said it in the clearest way but hopeful you get the picture.

[R0mai]

The += operator is not related to comparisons in any way. answer += i; is the same as answer = answer + i;

[Veight]

I knew I wasn't insane when using +=. Lol.

add: Although, looking at it. I isn't getting out of the if loop. If I put

if(i == prev1 + prev2)
		{
			prev1 = prev2;
			i = prev1;
			cout << i << endl;

All it shows is 1. :\

[R0mai]

What are you trying to do anyway?

[Veight]

Find the sum of all the even-valued terms in the Fibonacci sequence which do not exceed four million.

[Blessman11]

dude functions don't work in loops unless you are inside a while loop or you've decided to use a while loop instead

[R0mai]

dude functions don't work in loops unless you are inside a while loop or you've decided to use a while loop instead

Huh? Could you explain this, in more understandable form?

EDIT: Is 4613732 the correct answer? It would be interesting to calculate it in constant time.

[Veight]

I am looking over my code and realized that I will never get out of if(i == prev1 + prev2) because I am setting i = prev1 in that loop. Not sure how to go about rewriting this besides scrapping it. Heh.

[Blessman11]

Sorry I'm still getting confused about calling expressions like (if, while, do...) function, sorry but I'm still trying to loose the habit.

Anyway

I've noticed that if(){} statements seem to only execute once if they are out side a do or while loop.

eg

#include<iostream>
void main()
{
using namespace std;

bool boolean = true;
int intexample = 1;

if (boolean == 1)
{++intexample;
cout << intexample << endl;
}

system("PAUSE");
}

whereas for while loops, its the if statement gets executed multipletimes

#include<iostream>
void main()
{
using namespace std;

bool boolean = true;
int intexample = 1;

while(boolean == true)
{
if (boolean == 1)
{++intexample;
cout << intexample << endl;

if(intexample >= 20)
{
system("PAUSE");
}
}
}

system("PAUSE");
}

try these out and you'll see the point