C++ program

[laserpp]

Hey everyone, I am very confused on why my program is not working. It is suppose to run through a loop give a Fahrenheit Temp 0-20 and displaying the Celsius Temp next to each one. I am suppose to call the Celsius value from a function. Here is what i have:

#include <iostream>
using namespace std;


int celsius(int);

int main()
{

	int c;

	for (int x = 0; x <= 20; x++)
	{
		c = celsius(x);
		cout << "The Temperature in Fahrenheit is " << x << "	   The Temperature in Celsius is " << c << endl;
	}

	return 0;
}

int celsius(int x)
{
	return ((5/9)(x - 32));
}

What i get is the Fahrenheit temp going from 0-20 but the Celsius is always 0? Everything looks correct after look at similar examples from my book.

 

[Bruceification73]

need to use double instead of int, and change all of the values to whatever.0

Also last part should be ((5.0/9.0)*(x-32.0));

And actually it doesn't really work at all the way you have it set up. Try this:

#include  <iostream>
using namespace std;

int main()
{
	double x , c;
	for(x=0;x<21;x++)
	{
	c = (5.0 / 9.0) * (x - 32.0);
	cout<<"The temperature in fahrenheit is: "<<x<<"\tThe temperature in celsius is: "<<c<<endl;
	}
	system("pause");
	return 0;
}

This is working for me.

 

[Bruceification73]

But you may want to use higher values for X, because with 0-20 you get all negative numbers for C.

 

[laserpp]

Thanks, I cant use higher values, its a HW assignment and has to be 0-20, and I need to use functions. but will try some of the stuff you said. I have written other programs but more complicated functions and they work but this one is owning me.

 

[laserpp]

Okay, tried to change it up a little but still no luck.

#include <iostream>
using namespace std;


double celsius(int);

int main()
{

	double c;

	for (int x = 0; x <= 20; x++)
	{
		c = celsius(x);
		cout << "The Temperature in Fahrenheit is " << x << "	   The Temperature in Celsius is " << c << endl;
	}

	return 0;
}

double celsius(int x)
{
	double total;
	total = ((5/9)*(x - 32));
	return total;
}

Here is the output:

 

[Bruceification73]

This works:

#include <iostream>
using namespace std;

double celsius(int x);

int main()
{

	double c;

	for (int x = 0; x <= 20; x++)
	{
		c = celsius(x);
		cout << "The Temperature in Fahrenheit is " << x << "	   The Temperature in Celsius is " << c << endl;
	}
	system("pause");
	return 0;
}

double celsius(int x)
{
	double total;
	total = ((5.0/9.0)*(x - 32.0));
	return total;
}

 

[Bruceification73]

Just changed int to int x in the function call and added .0 to the values.

 

[flamethrower205]

I think important takeaway from this (and I see this error all of the time; it's very common) is the distinction between double and int arithmetic. The compiler evaluates everything within parenthesis first, so a statement such as (5/9) will be treated as integer arithmetic rather than double. This means that 5/9 = 0, so that the rest of your calculation will be zeroed out. Another common mistake is when a programmer wishes to take steps between two ints a and b and decides that the step size should be
double step = (b - a) / (numSteps - 1)
The intended result is for a double, but all of the arithmetic is done as ints, so that step usually becomes 0. The solution is to ask for
(b - a) / (numSteps - 1.0)
This works because the rule of thumb is that when doing arithmetic between a double and an int, the int gets upgraded to a double. However, as mentioned above, (5/9) is int/int, which is just 0.
Hope this clarifies things!

 

[Bruceification73]

yeah, I always use double if decimals will be involved or if there's math like he had.

 

[flamethrower205]

The beauty is what happens when you have untyped languages, like python. Then all sorts of heinous arithmetic errors happen cause of variable confusion.

 

[Bruceification73]

Yeah, I don't have too much experience with python, but I can imagine how it would be a lot different.

 

[laserpp]

worked like a charm thank you all very much. Was working for like 6 hours on multiple programs and just forgot about needed .0 for doubles =D

 

[Bruceification73]

Select best answer then?

 

[laserpp]

Best answer selected by laserpp.

 

[Bruceification73]

Danke. Glad to be of help.