Beginner's Calculator: Problem with expressions

Hello.

I'm new to C Programming and am struggling with a practice exercise for a course I'm doing. My aim is to code a simple calculator, which has two constants, two variables that are manually input, and an answer. Then there is a statement at the end showing my two input values and the answer to the calculation.

I just don't know how to get this to work.

Code:

`#include <iostream>`

using namespace std;

int main () {

//variable declarations and initialisation

const double mol = 1.0;

const double gas_const = 8.315;

char temp[50], vol[50], pres[50];

//prompt and read

cout << "Please enter the temperature / K:" << endl;

cin >> temp;

cout << "Please enter the volume / m^3:" << endl;

cin >> vol;

//calculate pressure

pres = (mol * gas_const * temp) / vol;

//print result

cout << "One mole of gas at " << temp << "K, in a volume of " << vol << "m^3, has a pressure of " << pres << "Pa." << endl;

} //end of main()

The calculator uses the expression P = nRT/V, where n and R are constants that I define in the program, and T and V are variables that I input manually.

This coding gives a single error on the line with the equation:

Code:

`error C2297: '*' : illegal, right operand has type 'char [50]'`

Both "pres" and "temp" have red lines underneath. When I move the cursor over "pres" I get **"Error: expression must be a modifyable lvalue"**, and doing the same with "temp" gives **"Error: expression must have arithmetic or enum type"**.

I've been working on this for almost four hours at the time of posting. I've Googled and searched through books, I've gone through my notes, but I don't understand what I'm supposed to do.

If I remove the expression and give "pres" a fixed value, the statement at the end works. Its the expression part that I don't understand.

Could anyone help me with this? Any help would be very much appreciated.

Thanks.