CODEWITHSUNDEEP
c++methodsparameters
AngryDuck
AngryDuck

Reputation: 4607

Passing parameters to a method C++

I have experience in java and I have decided to look at C++. To do this, I thought I'd go through some early (basic) Java examples I have done before, and convert them into C++. Basically I have two classes, 'main' and 'Conversion'

Conversion will convert imperial measurements to kilos.

main gets user input. What I'm trying to do, is pass 2 double values and two strings from main to a method in conversion convert but im getting the error

missing ';' before ',' for the method call below ( unit1 and unit 2 are double variables) and then other two are strings 

   Conversion.convert(unit1, unit2, sUnit1, sUnit2);

this is supposed to send the 4 parameters to this method in conversion.

void convert(double unit1, double unit2, std::string sUnit1, std::string sUnit2)
{
    double result1 = calculate(unit1, sUnit1);
    double result2 = calculate(unit2, sUnit2);
    print(result1+result2);
}

Any ideas why this throws an error? Also say if u need more code, I'm sure this is really obvious but maybe you can see from my code I'm more used to Java.

Upvotes: 0

Views: 439

Answers (1)

juanchopanza
juanchopanza

Reputation: 227370

You cannot call methods on classes like that. Either convert is a static method, in which case you call it like this:

Conversion::convert(unit1, unit2, sUnit1, sUnit2);

or it is a member function, in which case you need to call it on an instance of Conversion:

Conversion c;
c.convert(unit1, unit2, sUnit1, sUnit2);

Note that, unlike Java, in C++ you can have "free" functions, i.e. you do not have to place them inside a class. The common practice in these cases is to put functions in namespaces:

namespace Conversions
{
   void convert(double d1, double d2, std::string s1, std::string s2) { ... }
}

You can then call it similarly to the static method case:

Conversions::convert(unit1, unit2, sUnit1, sUnit2);

Also note that, unless you are going to make copies of the std::strings you are passing to the function, it is better to pass by const reference to avoid unnecessary copies:

void convert(double d1, double d2, const std::string& s1, const std::string& s2);

The same applies to the doubles, you can pass them by const reference, but it is hardly worth it given the cost of potentially copying a double.

Finally, main is the name of a very special function in C++ and C, so you should avoid using it for class names. It is not a keyword, but it could be confusing nonetheless.

Upvotes: 10

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