problem with if statements

xcajun_ · #1 11-Mar-2010, 17:10

this is soposed to be an all in one convertion program it runs just dosent do what i want it to. The problem is thats is going in order from 1 to 2 to 3. But i want it to jump to what number you type not for it to just run from begging to end. how do i get the if statements to work correctly? This is not homework for school im learing c++ on my free time.

CPP / C++ / C Code:

#include <iostream>
#include <cmath>

using namespace std;

int main()
{
    
double convertion;
double answer;
double feet;
double inches;
double meters;
double yards;
double miles;



       cout << "This is an all in one converter!" << endl; 
       cout << "Press 1 for feet into inches!" << endl;
       cout << "Press 2 for inches into feet!" << endl;
       cout << "Press 3 for meter into feet!" << endl;
       cout << "Press 4 for feet into meter!" << endl;
       cout << "Press 5 for feet into miles!" << endl;
       cout << "Press 6 for miles into feet!" << endl;
       cout << "Press 7 for meters into miles!" << endl;
       cout << "Press 8 for miles into meters!" << endl;
       cout << "Press 9 for inches into meters!" << endl;
       cout << "Press 10 for meters into inches!" << endl;
    
       cin >> answer;

         if (answer == 1);  
       cout << "Please enter the amount of feet you wish to convert!" << endl;
       cin >> answer;       
       convertion = answer * 12;       
       cout << "this is " << convertion << " inches" << endl;
       
       
        if (answer == 2);  
cout << "Please enter the amount of inches you wish to convert!" << endl;
       cin >> answer;          
       convertion = answer / 12;
       cout << "this is " << convertion << " feet" << endl;
     
    
       if (answer == 3);         
 cout << "Please enter the amount of meters you wish to convert!" << endl;
   cin >> answer;      
      convertion = answer * 3.280;      
      cout << "This is " << convertion << " feet";
      
       cin.get();
       cin.get();
}

Blake · #2 11-Mar-2010, 17:31

You have semicolons after all your if statements, which means that they won't actually have any effect. Those semicolons all need to go:

CPP / C++ / C Code:

if (answer == 1)

That does not fix your problem, though. Now if you enter something other than 1, the line immediately after the if statement will not be executed, but everything after that will be. Curly braces will solve that problem:

CPP / C++ / C Code:

	if (answer == 1)
	{
		cout << "Please enter the number of feet you wish to convert!" << endl;
		cin >> answer;       
		conversion = answer * 12;       
		cout << "this is " << conversion << " inches" << endl;
	}

Finally, you only want one to do one conversion, so you should use if-else statements:

CPP / C++ / C Code:

	if (answer == 1)
	{
		cout << "Please enter the number of feet you wish to convert!" << endl;
		cin >> answer;       
		conversion = answer * 12;       
		cout << "this is " << conversion << " inches" << endl;
	}
	else if (answer == 2)
	{
		cout << "Please enter the number of inches you wish to convert!" << endl;
		cin >> answer;          
		conversion = answer / 12;
		cout << "this is " << conversion << " feet" << endl;
	}
        else if (answer == 3)
	{
		cout << "Please enter the number of meters you wish to convert!" << endl;
		cin >> answer;      
		conversion = answer * 3.280;      
		cout << "This is " << conversion << " feet";
	}

Some other tips:

You may want to consider using a switch statement because they were designed for this kind of thing.

It's not a great idea to use the same variable to store the menu selection result and measurement to convert. You should probably make a different variable (an int) for the menu selection.

If you wanted to consider a larger set of conversions, manually coding every possible conversion would not be a good idea. It would be better to pick a unit for internally storing distances, convert the input units to the internal units, and then convert the internal units to the output units. For example, if you choose to use feet internally, you might store two constants inchesToFeet and milesToFeet. Then the conversion from inches to miles would be would be:

CPP / C++ / C Code:

const double inchesToFeet = 12.0;
const double milesToFeet = 1.0/5280.0;
//...
conversion = answer*inchesToFeet/milesToFeet;

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problem with if statements

Re: problem with if statements