How to make my program shorter using arrays or other method?

[freiheit1991]

Hello Everyone
This is just part of my code, this small program converts units from one to another (for example: tons to kilograms and vice-versa). Since I included different types of conversion like temperature, currency, size, etc using this same method below... my program has grown up to 3500 lines, and I am sure there is a way to make it smaller, I read about arrays I understand the basic of it and how to program basic examples with it but I do not know how to include arrays in my program to make it shorter, and if there is any other way I would love to hear from it, I have been stuck for a while already also because I did not have enough time to program but I will really appreciate if somebody can help me how to continue improving my coding, thanks in advance.

The program runs perfectly fine like I wanted, its just the size that bugs me, the efficiency and maintainability of the code.

  double startMU()
{
	char answerExit = 'y';
	string unit1;
	string unit2;
	double amount;
		
	const double tn_kg = 1000;   const double tn_lb = 2204.62;     const double tn_oz = 35274;     const double lb_oz = 162;
	const double kg_tn = 0.001;  const double lb_tn = 0.000453592; const double oz_tn = 2.835e-5;  const double oz_lb = 0.06252;
	const double kg_g = 1000;    const double kg_lb = 2.20462;     const double kg_oz = 35.274;
	const double g_kg = 0.001;   const double lb_kg = 0.453592;    const double oz_kg = 0.0283495;
	const double tn_g = 1e+6;    const double g_lb = 0.00220462;   const double g_oz = 0.035274;
	const double g_tn = 1e-6;    const double lb_g = 453.592;      const double oz_g = 28.3495;

	const double tn_tn = 1; const double lb_lb = 1;
	const double kg_kg = 1; const double oz_oz = 1;//25
	const double g_g = 1;
	
	printMUmenu();

LOOP_massUnits:
	do {
			cout << "\n Insert unit to convert: ";
			cin >> unit1;
			cout << " Insert unit to obtain: ";
			cin >> unit2;
			if (unit1 == "tn" && unit2 == "kg")
			{
				cout << "\n How many " << unit1.c_str() << " do you want to convert? ";
				cin >> amount;
				cleanCin();
				cout << " " << amount << " " << unit1.c_str() << " are " << amount * tn_kg << " " << unit2.c_str() << ".\n";
			}
			else if (unit1 == "kg" && unit2 == "tn")
			{
				cout << "\n How many " << unit1.c_str() << " do you want to convert? ";
				cin >> amount;
				cleanCin();
				cout << " " << amount << " " << unit1.c_str() << " are " << amount * kg_tn << " " << unit2.c_str() << ".\n";
			}

			/*...and so on with 26 possible combinations in total...*/

			else if (unit1 != "tn", "kg", "g", "lb", "oz" && unit2 != "tn", "kg", "g", "lb", "oz")
			{
				cout << "\nERROR: Invalid Unit\n";
				goto LOOP_massUnits;
			}
	} while (answerExit != 'y');
	return 0;
}

[AbstractionAnon]

A few comments:

Line 47: Get rid of the goto. Gotos should be avoided. They result in spaghetti code. You already have a loop. Use a continue statement to go to the top of the loop.

Lines 29: There is no reason to take a c_str() of a string. You can use a string (unit1) directly in a cout statement.

Line 44: Your if statement is faulty. You can not have implied left side of a comparison. Each comparison must be fully specified.

else if (unit1 != "tn" && unit1 != "kg" && unit1 != "g" && unit1 != "lb" && unit1 != "oz" ... etc ) 

I would suggest using a std::map.

 
  std::map<string, double>  factors {"kg_tn", 0.001, "tn_kg", 1000, ... }
  // Initialization syntax requires C++11 

Now all you have to do is build a key which is the concatenation of the from and to units.

  string key;
  key = unit1 + '_' + unit2;

Then look that up in the map.

 
  std::map<string,double>::const_iterator citer;
  double factor;

  citer = factors.find (key);
  if (citer == factors.end()
  {   //  not found  }
  else
  {  factor = citer->second;
      // cout conversion message
  }

All your if/else statements go away.

[keskiverto]

Look at the description of std::map at the Reference section.

Lets make a simpler table:

tn 1e+6
kg 1000.0
lb  453.6
oz   28.4
 g    1.0

You do get input amount and unit.

You can look up the unit from the table. If the input is not in the table, then it is invalid. Use a while-loop to get valid input. Do not use goto. While 'goto' may appear "simple", it actually makes program more complex and error-prone.

Now you have a valid unit. The table has a corresponding value. If you do multiply the amount with the value, you do perform a conversion to what unit?

Then you have the output unit and its corresponding value. If you divide the result of previous multiplication with the output-value, you again convert the unit. From what to what?

It is an extra optimization to handle the input==output non-conversions.


Why do you print the std::strings as C-strings?