Pass by value, reference

[2EURX9L8]

This is just not sinking in no mater how much I go over my text and this site.
I am completely lost using these, I need to write 4 functions including main to display a report with the size of room in square, feet cost of carpet,cost to install the carpet.

This is my code so far, could someone take a glance and maybe help me understand this concept better?


#

[ReedTompkins]

Is your question about how the code works, or about the difference between pass by value and pass by reference?

[zb0S216C]

I take it you don't understand references?

Simply, a reference is NOT! an object, but just an alias. When you initialise a reference to object (a reference MUST! be initialised), the reference becomes an alternative name for the assigned object. For example:

int object( 10 );
int &ref( object );

In this code, ref becomes another name for object. So any changes made to ref affect object. The object referred to is called a referent.

When a reference has been initialised, the reference cannot be re-assigned to another object. Effectively, it's similar to this pointer declaration: int * const ptr( &... ). Note that a pointer IS NOT! a reference.

Now, when references are used as parameters, the same thing happens as the above code. For example:

void basic_function( const int &ref_param )
{ 
    ... 
}

int main( )
{
    int object( 10 );
    ::basic_function( object );
}

When object is passed to basic_function( ), ref_param refers to object. Specifically, ref_param refers to the argument you give it.

Note that a constant reference, like the parameter in the above code, can refer to literals (magic constants), such as 10, 'A', 3.14, and "String". These are called symbolic constants.

_Wazzak

[cire]

while(width,length, carpetCost<=0)

That effectively evaluates to:

while ( carpetCost <=0 )

You want:

while (width <=0 || length <=0 || carpetCost <=0)

By the same token:

cin>>width, length, carpetCost;}

is the same as

(cin >> width), length, carpetCost;

You probably want something closer to:

cin >> width >> length >> carpetCost;

[2EURX9L8]

Thank you for your input guys, I do appreciate it but I am am still lost.

How do you use pass by value/reference with multiple values and used by multiple functions then report single values from those multiple value functions in main?????

[chipp]

you delete the code?

[2EURX9L8]

some of it, I just have been going at it for a couple of hours changing it trying other things, then changing back, then back again ect...

[chipp]

btw, your function could be more simpler:

void getInput(double &width, double &length, double &carpetCost)
		{	//double width, length, carpetCost;
	
			cout<<"please enter the width: "<<endl;
			cin>>width; 
			while(width<=0)
				{cout<<"Error, please enter a width with a postive value: ";
				cin>>width;}
		
			cout<<"please enter the length: "<<endl;
			cin>>length;
			while(length<=0)
				{cout<<"Error, please enter a length with a postive value: ";
				cin>>length;}
			
			cout<<"please enter the price of the carpet: "<<endl;
			cin>>carpetCost;
		    while(carpetCost<=0)
				{cout<<"Error, please enter a price with a postive value: ";
				cin>>carpetCost;}
			
			return;
		
		}

turns like:

void getInput(double &width, double &length, double &carpetCost) {
	//double width, length, carpetCost;
	do {
		cout << "please enter a positive values for all the variables...";
		cout << "enter widhth: ";
		cin >> width;
		cout << "enter length: ";
		cin >> length;
		cout << "enter the carpet cost: ";
		cin >> carpetcost;
	} while (width <= 0 || length <= 0 || carpetcost <= 0);
	return;
}

"trimmed" my way haha...

[2EURX9L8]

yeah I changed it and I think I copied and pasted an old version. Thanks though. What about the functions? how do I un cluster $@# it and get it to work?

[polar]

i am just going to use your own code to show you your mistake

#include <iostream>
#include <iomanip>

using namespace std;
void getInput(double, double&, double&);
double computeArea(double length, double width);
void computeCosts(double& area,double& carpetCost);

	const int INCHESPERSQUARE=144;
	

	int main(){
		
			double width, length, carpetCost,totalArea,totalInstallcost;
			cout<<"\t\tAce Carpet Company Cost estimate\n\n";
			//getInput(width,length,carpetCost);
			cout<<"The area in square feet is: "<<totalArea;
			cout<<"The cost of the carpet is: "<<carpetCost++<<endl;
			cout<<"The cost to install the carpet is "<<totalInstallcost++<<endl;
	
	}		

	void getInput(double &width, double length, double &carpetCost)
		{	//double width, length, carpetCost;
	
			cout<<"please enter the width: "<<endl;
			cin>>width; 
			while(width<=0)
				{cout<<"Error, please enter a width with a postive value: ";
				cin>>width;}
		
			cout<<"please enter the length: "<<endl;
			cin>>length;
			while(length<=0)
				{cout<<"Error, please enter a length with a postive value: ";
				cin>>length;}
			
			cout<<"please enter the price of the carpet: "<<endl;
			cin>>carpetCost;
		    while(carpetCost<=0)
				{cout<<"Error, please enter a price with a postive value: ";
				cin>>carpetCost;
cout<<"please enter the install cost<<install cost--";
cin>>"instal cost"}
while(width<=0,length<=0,carpet cost<=0);
			return(0);
while(width>>0,length>>0,carpetcost>>0);
return(carpet cost);
		
		}

i used pass by reference it is much easier to master and use considering that u will just need to know what you are passing and use some constructor and a destructor in the next class or function u want to call it in

[2EURX9L8]

well thank you all for helping my worn out brain

[zb0S216C]

I've had a go at writing you code. I've omitted the body of computeCosts( ) and computeArea( ) to give you something to chew on.

#include <iostream>
#include <iomanip>
#include <limits>

//
// P R O T O T Y P E S
//

/* get_input( ): Obtains the users values. */
void get_input( double &width, double &length, double &cost );

/* compute_area( ): Computes the area based on the specified width and length. */
double compute_area( const double &width, const double &length );

/* compute_costs( ): Computes the total amount based on area and cost. */
void compute_costs( const double &area, double &cost );

//
// C O N S T A N T S
//

/* INCHES_PER_SQUARE: Used for the computation of the area. */
const unsigned int INCHES_PER_SQUARE( 144U );

//
// M A I N  -  E N T R Y   P O I N T
//

int main( )
{
    //
    // L O C A L   O B J E C T S
    //

    double width( 0.0 ),
           length( 0.0 ),
           carpet_cost( 0.0 ),
           total_area( 0.0 ),
           total_install_cost( 0.0 );

    /* Display the program's title. */
    std::cout << "\t\tAce Carpet Company Cost estimate\n\n";

    /* Retrieve the user's input. */
    ::get_input( width, length, carpet_cost );

    /* Perform all relevent computations */
    ::compute_costs( ::compute_area( width, length ), carpet_cost );

    /* Display all relevant information regarding area and cost. */
    std::cout << "The area in square feet is: " << total_area << std::endl;
    std::cout << "The cost of the carpet is: " << carpet_cost << std::endl;
    std::cout << "The cost to install the carpet is " << total_install_cost << std::endl;

    /* Give the user a chance to see the result. */
    std::cin.ignore( std::numeric_limits< std::streamsize >::max( ), '\n' );
    return( 0 );
}

/* Definition Of: get_input( )
 *
 * [O] width:  Stores the users requested width.
 * [O] length: Stores the users requested length.
 * [O] cost:   Stores the users requested cost.
 */
void get_input( double &width, double &length, double &cost )
{
    while( width < 1U )
    {
        std::cout << "please enter the width: ";
        std::cin >> width;
    }

    while( length < 1U )
    {
        std::cout << "please enter the length: ";
        std::cin >> length;
    }

    std::cout << "please enter the price of the carpet: ";
    std::cin >> cost;
}

/* Definition Of: compute_area( )
 *
 * [I] width:  The requested width.
 * [I] length: The requested length.
 */
double compute_area( const double &width, const double &length )
{
    return( 0.0 );
}

/* Definition Of: compute_area( )
 *
 * [I] area: The area of the floor.
 * [O] cost: Stores the price per inch.
 */
void compute_costs( const double &area, double &cost )
{
}

_Wazzak