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C++/Exponents

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Hi, I'm trying to write a pretty basic calculator and I want to make it to where I can have exponents.  The calculator has 3 functions: main, greeting, calculations. I have main that calls on greeting and then calculations.  Calculations first asks which type of calculation would you like to do.  Then it defines int a and then the code accepts a (cin >> a;).  So then this runs:

   if(a == 1)
   {
        //Adding
        cout << "You've chosen adding!" << endl;
        cout << "Type two numbers and they'll add together." << endl;
        double b;
        double c;
        cin >> b;
        cin >> c;
        cout << b + c << endl;
   }
   else if(a == 2)
   {
        //Subtracting
        cout << "You've chosen subtracting!" << endl;
        cout << "Type two numbers and they'll subtract the first one from the second." << endl;
        double b;
        double c;
        cin >> b;
        cin >> c;
        cout << b - c << endl;
   }
   else if(a == 3)
   {
        //Multiplying
        cout << "You've chosen multipling." << endl;
        cout << "Type two numbers and they'll multiply by each other." << endl;
        double b;
        double c;
        cin >> b;
        cin >> c;
        cout << b * c << endl;
   }
   else if(a == 4)
   {
        //Dividing
        cout << "You've chosen dividing." << endl;
        cout << "Type two numbers and they'll divide by each other." << endl;
        double b;
        double c;
        cin >> b;
        cin >> c;
        cout << b / c << endl;
   }
   else if(a == 5)
   {
        //Exponents
        cout << "You've chosen exponents." << endl;
        cout << "Type two numbers and your first one will be that first number, and the second will be the exponent." << endl;
        double b;
        double c;
        cin >> b;
        cin >> c;
        cout << b ^ c << endl;

I need to know how to make the last else if statement to be able to run b(to the power of)c.

Hope you can help :)

Answer
Well although C and C++ have no exponentiation operator such as ^ in BASIC or ** in FORTRAN it does include a maths function to do it. [Note: in C and C++ the ^ symbol is used for the bitwise exclusive OR operator].

The function is called pow, is considered part of the maths section of the C/C++ standard library so you need to include <cmath> (Or <math.h> for C and really old C++ libraries). You may have to explicitly link to a math library (e.g. use option -lm for g++/gcc and some other Linux / Unix compilers) to get your program to complete building.

The pow function takes a floating point base and a floating point exponent or power and returns a floating point result:

   // Replacement for your program line:
   // cout << b ^ c << endl;
   cout << pow( b, c ) << endl;    


Hope this helps and moves you forward.  

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Ralph McArdell

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I am a software developer with more than 15 years C++ experience and over 25 years experience developing a wide variety of applications for Windows NT/2000/XP, UNIX, Linux and other platforms. I can help with basic to advanced C++, C (although I do not write just-C much if at all these days so maybe ask in the C section about purely C matters), software development and many platform specific and system development problems.

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My career started in the mid 1980s working as a batch process operator for the now defunct Inner London Education Authority, working on Prime mini computers. I then moved into the role of Programmer / Analyst, also on the Primes, then into technical support and finally into the micro computing section, using a variety of 16 and 8 bit machines. Following the demise of the ILEA I worked for a small company, now gone, called Hodos. I worked on a part task train simulator using C and the Intel DVI (Digital Video Interactive) - the hardware based predecessor to Indeo. Other projects included a CGI based train simulator (different goals to the first), and various other projects in C and Visual Basic (er, version 1 that is). When Hodos went into receivership I went freelance and finally managed to start working in C++. I initially had contracts working on train simulators (surprise) and multimedia - I worked on many of the Dorling Kindersley CD-ROM titles and wrote the screensaver games for the Wallace and Gromit Cracking Animator CD. My more recent contracts have been more traditionally IT based, working predominately in C++ on MS Windows NT, 2000. XP, Linux and UN*X. These projects have had wide ranging additional skill sets including system analysis and design, databases and SQL in various guises, C#, client server and remoting, cross porting applications between platforms and various client development processes. I have an interest in the development of the C++ core language and libraries and try to keep up with at least some of the papers on the ISO C++ Standard Committee site at http://www.open-std.org/jtc1/sc22/wg21/.

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