# Troubleshooting C++ Circle Area Calculation

• C/C++
• JamesU
In summary, the programmer has made a mistake with their code. They have not properly specified the values for the variables, and as a result, the program produces incorrect results.
JamesU
Gold Member
What's wrong with this C++ project I'm working on? it's supposed to find the area of a circle:

#include <cstdlib>
#include <iostream>

using namespace std;

int main(int argc, char *argv[])
{
int pi = 3.14
int rad
int radsqr = rad*rad
cout << "radius of the circle:" <<
cin >> rad
cout >> "The radius of the circle is about:" << radsqr*pi << end1;

system("PAUSE");
return EXIT_SUCCESS;
}

It's been a while since I've done programming, but looking at it quickly, I just notice that you said int pi =3.14, but int only stores integers so your really saying int pi =3 . This may not be the only problem, but its the one that I see.

Ahh what a mess! Try this:

Code:
double pi = 3.14 ;
double rad ;
cout << "radius of the circle:" ;
cin >> rad ;
cout << "The radius of the circle is about:" << rad*rad*pi << endl ;

Last edited:
oh, I meant 'the area of the circle is about:'

but thanks.

Oh, and you square rad before it gets the input from the user. That means that since rad starts out as random garbage before you give it a value, radsqr is random garbage squared. You have to square it after the line that says cin<<... to get what you want. So if you make that change and change the int's to float's it should work.

grrr...Now I can't get the circumference to show up:
Code:
#include <cstdlib>
#include <iostream>

using namespace std;

int main(int argc, char *argv[])
{

double pi = 3.14 ;
int rad ;
cout << "radius of the circle:" ;
cin >> rad ;
cout << "The area of the circle is about:" << rad*rad*pi << endl;
cout << "The circumference of the circle is about:" << rad*2*pi <<
system("PAUSE");
return EXIT_SUCCESS;
}
it only displays the area

Actually you probably want rad to be double too since you can have decimal values.

Why do you have a hanging << at the end of the circumference line? Dont' forget the endl;

it says:

stupid dev C++ said:
end1' is undeclared (first use this function)
:grumpy:

It's endl, not end1(end-lowercase L, not end-one)

Its the letter "L", but lower case. Not the number "1"

oh, I'm stupid. It's the font on my compiler that's confusing me

my formula calculation is complete:

Radius of the circle: 3
The area of the circle is about: 28.26
The circumference of the circle is about: 18.84
The diameter of the circle is: 6

muahaha

Congrats! Now try something more difficult like calculate pascal's triangle.

I'll work my way up.

what was pascal's triangle? the 3/4/5 one? in trig?

aha! basic trig

Code:
#include <cstdlib>
#include <iostream>

using namespace std;

int main(int argc, char *argv[])
{
double hyp
double opp
double adj
cout << "Input sides of a right triangle
cout << "Hypotenuse:" << endl;
cin >> hyp
cout << "opposite" << endl;
cin >> opp
cout << "adjacent" << endl;
cin >> adj
cout << "Triangle's properties are:" << endl;
cout << "Sine:" adj/hyp " Cosine:" opp/hyp " Tangent:" opp/adj
system("PAUSE");
return EXIT_SUCCESS;
}

unfortunately, I do not understand that

The flaw in my trig program is that anyone can put the hypotenuse as a smaller length than the opposite or adjacent sides. could I do an if statement that if this happens, function main() will execute again?

Or you could just have a loop that continues to ask for the hypotenuse until it is an accepatable value.

something like?

for ((hyp<opp)||(hyp<adj))
{
cin >> hyp
}

A do while loop would be appropriate:

do {
cin >> hyp ;
} while ( (hyp < opp) || (hyp<adj) ) ;

okay, and where would I put it in the code? right after sin cos and adj are specified, right?

Well, in order to compare hyp you need to know the value of opp and adj, so after you get those to values then you can stick the above code in.

Programming is a logical process. Whatever the flow of the code, it has to make sense. You can't just be comparing variables that don't have any specified value.

now it says that there should be a semicolon before the variable declaration, like:

;double

and it says that on that same line, there's a missing terminating character.

Code:
#include <cstdlib>
#include <iostream>

using namespace std;

int main(int argc, char *argv[])
{
double hyp
double opp
double adj
cout << "Input sides of a right triangle
cout << "Hypotenuse:" << endl;
cin >> hyp
cout << "opposite" << endl;
cin >> opp
cout << "adjacent" << endl;
cin >> adj
#include <cstdlib>
#include <iostream>

using namespace std;

int main(int argc, char *argv[])
{
double hyp
double opp
double adj
cout << "Input sides of a right triangle
cout << "Hypotenuse:" << endl;
cin >> hyp
cout << "opposite" << endl;
cin >> opp
cout << "adjacent" << endl;
cin >> adj
cout << "Triangle's properties are:" << endl;
cout << "Sine:" adj/hyp " Cosine:" opp/hyp " Tangent:" opp/adj
system("PAUSE");
return EXIT_SUCCESS;
}
cout << "Triangle's properties are:" << endl;
cout << "Sine:" adj/hyp " Cosine:" opp/hyp " Tangent:" opp/adj
system("PAUSE");
return EXIT_SUCCESS;
}`

In order to get a better precision in your pi-value than 3.14, a common strategy is to define your pi as follows:

double pi=4*atan(1);

Where atan is the arcus-tangent function.
If your machine doesn't accept "atan()", try arctan() instead.

can anyone help with my trig functions?

## 1. How do I fix my C++ code to calculate the area of a circle?

To fix your code, make sure you are using the correct formula for calculating the area of a circle, which is A = πr^2. Also, ensure that you have properly declared and initialized your variables and that you are using the correct data types. Additionally, double check your code for any syntax errors or logic mistakes.

## 2. Why is my C++ program not calculating the area of a circle correctly?

There could be several reasons for this. Check to make sure that your input values are correct and that you are using the correct formula. Also, check for any potential errors in your code such as incorrect variable names or missing parentheses. Consider using debugging tools or printing out intermediate values to help identify the issue.

## 3. How can I optimize my C++ code for calculating the area of a circle?

To optimize your code, consider using built-in functions or libraries for calculating the area of a circle instead of writing your own formula. Additionally, try to minimize the number of unnecessary calculations or variables in your code. Finally, consider using more efficient data types, such as float or double, if precision is not critical.

## 4. Can I use the same code to calculate the area of other shapes?

No, the formula for calculating the area of a circle is specific to circles only. Other shapes, such as squares or triangles, have different formulas for calculating their areas. However, you can reuse some parts of your code, such as declaring and initializing variables, for other shape calculations.

## 5. How can I handle errors or invalid inputs in my C++ program for calculating the area of a circle?

You can use conditional statements or try-catch blocks to handle errors or invalid inputs in your code. For example, you can check if the user has entered a negative radius or a non-numeric value and prompt them to enter a valid input. You can also use exceptions to handle any potential errors that may occur during the execution of your code.

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