Thread: Beginner needs help (calculator for serial/parallel electric circuits)

I started working on C++ last week and the teacher asked us to write a program that will calculate the total resistance of an electric circuit (both in serial and parallel).

Both serial and parallel work fine, but the thing that bugs me is that I need to block/filter the 0 and negative values so the total resistance in parallel doesn't give me an invalid answer.

I tried the if/else instruction but still doesn't work (I'm sure I did something wrong... gotta read more of my learning book )

I'd appreciate it if you guys can give me a hand here.

Here's my current code (sorry if it looks weird, I translated from french to english):

Code:

// Excercice #1

#include <iostream>

using std::cout;
using std::cin;

int main()
{
	double Rserial,
		   counterResistors,
		   Rvalue,
		   Rparallel,
		   TRparallel;

	Rserial = 0;
	counterResistors = 0;
	Rparallel = 0;

	cout << "Enter the value of the resistor (or enter -1 if done): "; 
	cin >> Rvalue;

	while ( Rvalue != -1 ) 
	{
			if ( Rvalue <= 0 )

		cout << "\nPlease, enter a valid resistor value! (or enter -1 if done): ";
		cin >> Rvalue;
	}

			else

                Rserial = Rserial + Rvalue;
		Rparallel = Rparallel + (1 / Rvalue);
		TRparallel = 1 / Rparallel;
		counterResistors = counterResistors + 1;

		cout << "\nEnter the value of the resistor (or enter -1 if done): ";
		cin >> Rvalue;
	}

	cout << "\n*The total resistance in serial is -> R = " << Rserial; cout << " Ohm(s)";
	cout << "\n*The total resistance in parallel is -> R = " << TRparallel; cout << " Ohm(s)\n\n";

	return 0;
}

Thanks in advance.

PS: In case you forgot your sciences class:

Serial = ValueResistor1 + ValueResistor2 + ValueResistor3 + ... + ValueResistorX
Parallel = 1 / ( 1/VR1 + 1/VR2 + 1/VR3 + ... + 1/VRX) -> Thus why we can't have 0 in this case.

Right - Brackets! You need to put brackets around all the lines that are to be affected by the if-statement. Without brackets, only one line following the if or else is affected.

And, make sure that you have matching-pairs of brackets.

Code:

while ( Rvalue != -1 ) 
{
     if ( Rvalue <= 0 )
          cout << "\nPlease, enter a valid resistor value! (or enter -1 if done): ";  // Depends on if-statement.
          cin >> Rvalue;    // This line will execute every time.


     else
          Rserial = Rserial + Rvalue;  //Depends on else-statement.
          Rparallel = Rparallel + (1 / Rvalue);  // Everything else executes every time!
          TRparallel = 1 / Rparallel;
          counterResistors = counterResistors + 1;

          cout << "\nEnter the value of the resistor (or enter -1 if done): ";
          cin >> Rvalue;
}

Code:

while ( Rvalue != -1 ) 
{
     if ( Rvalue <= 0 )
     {    // All of this is affected by the if-statement...
          cout << "\nPlease, enter a valid resistor value! (or enter -1 if done): "; 
          cin >> Rvalue;   
     }   //End of if-condition.


     else
     {   // All of this is affected by the else-statement...
          Rserial = Rserial + Rvalue; 
          Rparallel = Rparallel + (1 / Rvalue); 
          TRparallel = 1 / Rparallel;
          counterResistors = counterResistors + 1;

          cout << "\nEnter the value of the resistor (or enter -1 if done): ";
          cin >> Rvalue;
     }  // End of else-condition.

} //End of while-loop