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[Томму]

It's simple, someone posts an exercise, the other one solves it, and so on .
Okay, let's start.

Ohm's law Make a class describing a resistor with the following members:

Quote

• a private data member for the resistance, R
  
• a public member function to set the value of R
  
• a public member function to calculate the current I from the voltage E
  
• a public member function to calculate the voltage E from the current I
  
• a public member function to calculate the power dissipation P from the current I using the formula P = I·E, where E is calculated using the previous member function.

Make a program to test this class.

[nooc9]

#include <iostream>

class Resistor
{
   float R;
public:
   Resistor& setR(float r) { R=r; return *this; }
   float getI(float E) { return E/R; }
   float getE(float I) { return R*I; }
   float getP(float I) { return I*getE(I); }

   Resistor() :R(0) {}
   Resistor(float r) :R(r) {}
};

int main() {
   Resistor r(5);
   std::cout << "Resistor(5).getE(0.5) = " << r.getE(0.5f) << " V" << std::endl;
   std::cout << "Resistor(100).getI(12) = " << r.setR(100).getI(12) << " A" << std::endl;
   std::cout << "Resistor(1200).getP(0.01) = " << r.setR(1200).getP(0.01) << " W" << std::endl;
   return 0;
}

Ok, so here is a silly one from me.

Let Variables be a map of string to float:

typedef std::map<std::string,float> Variables;

Let Operation be an abstract class that has the following declaration:

struct Operation {
   virtual float evaluate(const Variables& vars) = 0;
};

Implement Add, Sub, Mul, Div, Const, Var that extend Operation so that the following example is possible:

// Create expression: (A+10)*(1/(B-3))
Mul expression(
	Add( Var("A"), Const(10) ),
	Div( Const(1),
		Sub(Var("B"),Const(3))
		)
	);

// Create variable map
Variables vars;
vars["A"] = 2.5;
vars["B"] = 7;

// Evaluate expression using variables in vars map
float result = expression.evaluate(vars);

You may add abstract methods to Operation.

Edited by nooc9, 28 October 2009 - 07:45 AM.