Retrieve the Value of An Integer Variable

This is probably easily figured out, but I can't find a solution anywhere, for some reason. Perhaps I'm not searching for the right thing. And maybe it's in some beginner tutorial I haven't watched.

Anyway, I was wondering how to retrieve the value of an integer variable in C++? I know you can use cin.getline() for string variables, but I received an error message when I attempted that with an integer var开发者_运维问答iable (and rightfully so, I know it was wrong, but I was looking for a solution).

My project is a Win32 console application. What I'm trying to do is ask a user to input a number, stored in the variable n. Then I take the value of n and perform various math functions with it. In my header file, I have string, windows, iostream, stdio, math, and fstream. Do I need to add another library?

EDIT:

cout << "TEST SINE";
cout << "\nPlease enter a number.\n\n";
cin >> n;
break;

Here's the code I'm trying to use. Is this all I need to do? If so, how do I incorporate the variable so I can test it using sin, cos, and tan?

Yet again, thanks ahead of time.

what is the problem with this?

cin>>n;

For math functions, float or double would be better option.

int main()
{
   double number;
   double result;

   cout<<"Enter a number:"<<endl;
   cin>>number;

   result = sin (number);  //if you consider number is in radians
   //result = sin(number*3.14159265/180.0) //if you consider number is in degrees    

   cout<<result;

   return 0;
}

If you want an integer, you can use:

cin >> n;

but you had better have control of the input data if you want a robust application.

Perhaps a better idea would be to input it as a string as you already know how to do with getline(), then validate that the string consists of all numeric characters before calling a conversion function like atoi() or strtol().

That way, you get robust input plus the data types you want.

But, if you want to use trigonometric functions, you're probably better off working with doubles, with atof(), rather than integers.

Here's a sample program to get you started:

#include <iostream>
#include <cstdlib>
#include <cmath>
#include <cstring>
using namespace std;

int main (void) {
    char s[256];

    // Get and check line.

    cout << "Enter angle in degrees: ";
    cin.getline(s,100);
    for (char *ps = s; *ps != 0; ps++) {
        if (!isdigit (*ps)) {
            cout << "Not numeric" << endl;
            return 1;
        }
    }

    // Output string, float, sine and cosine (convert to radians first).

    float f = atof (s);
    cout << "String : '" << s << "'" << endl;
    cout << "Float  : " << f << endl;
    f = f * 3.141592653589 / 180.0;
    cout << "Sine   : " << fixed << sin (f) << endl;
    cout << "Cosine : " << fixed << cos (f) << endl;

    return 0;
}

Sample runs shown below:

Enter angle in degrees: 30
String : '30'
Float  : 30
Sine   : 0.500000
Cosine : 0.866025

Enter angle in degrees: 45
String : '45'
Float  : 45
Sine   : 0.707107
Cosine : 0.707107

Enter angle in degrees: 90
String : '90'
Float  : 90
Sine   : 1.000000
Cosine : -0.000000      (caused by floating point inaccuaracy).