Codes runs once but not a second time

[parmih4]

It has been happening to me ever since I started writing codes.I write a code, it runs, gives me the right outcome and then the next time I run it again or rewrite the code it gives me weird answers or doesn't even work even though I basically copy and paste it. for example the code bellow...It doesn't work when it did a week ago. What is happening????

thanks for your help.

  #include <iostream>
using namespace std;
double sqrtnum( double num)
{
	double lower_bound=0;
	double upper_bound=num;
	double temp=0;
	while((temp*temp) - num > 0.01)
	{
		temp=(lower_bound + upper_bound)/2;
		if(temp*temp>=num)
			upper_bound=temp;
		else
			lower_bound=temp;
	}
	return num;
}
int main()
{
	int a,b,c;
	int delta;
	cout<<"enter 3 numbers"<<endl;
	cin>>a>>b>>c;
	delta=b*b - (4*a*c);
	if(delta>0)
	{
		cout<<"X1="<<((b+sqrtnum(delta) / 2*a))<<endl;
		cout<<"X2="<<((b - sqrtnum(delta) / 2*a))<<endl;
	}
	else if(delta==0)
	{
		cout<<"X="<<((b+sqrtnum(delta) / 2*a))<<endl;
	}
	else if(delta<0)
	{
		cout<<"No root"<<endl;
	}
	return 0;
}

[Ispil]

What IDE are you using?

Also, your sqrtnum function literally does nothing. It does not modify num- it just returns it.

[parmih4]

@Ispil How should I write it then?
And what is IDE?

[CS Student]

An IDE is an "Integrated Development Environment" It's basically a program that allows to make other programs. Some include: Visual Studios, Codeblocks, and lots others.

[parmih4]

Visual Studio...Yes...I use Visual Studio. and about the function...I'd appreciate if you helped me.

[CS Student]

Describe what exactly you are trying to do. Is the function just supposed to return the square root of a number?

[parmih4]

yes...the rest is to find the roots of a function which I don't have a problem with...But my sqrtnum is, as mentioned above, giving me wrong answers...

[CS Student]

I'm not sure. What I would do is start putting cout statements all over the place (or you can use asserts) and you might be able to figure it out that way. But honestly I don't know.

[parmih4]

Thanks anyways.

[Ispil]

Well, you actually don't need to make your own sqrt function. If you add #include <cmath> to the header, than the std library has a built-in square root function called sqrt. You can save all of the headway by just using that instead of trying to... well, create your own.

[dhayden]

Reread the first comment by ispil. Look at line 17. You are returning num, the value that you passed into the function. This is not the right thing to return.

[parmih4]

Should it return temp?
I changed it but it still gave me wrong answer