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how to use TEMPLATE in C++

1
I am new in C++, and learning the langauge by my self only, while practicing i come across one question for which i have no idea, the question is to calculate area and perimeter of rectangle, the code i wrote was


#include <iostream>
using namespace std;
int main ()
{
// declaration of variables
float length; //length of a rectangle
float width; //width of a rectangle
float area; //area of a rectangle
float perim; //perimeter of a rectangle
// prompt for and read the input values
cout << "Enter the length of the rectangle" << endl;
cin >> length;
cout << "Enter the width of the rectangle" << endl;
cin >> width;
//Calculate the area and the perimeter
area = length*width;
perim = 2.0*length + 2.0*width;
//Display the result
cout << "The area is " << area << endl;
cout << "The perimeter is " << perim << endl;

return 0;

}

BUT I WHAT I NEED IS

The program will read the values of length and width from the user trough keyboard and passes these values to the function calculate(T x, T y). The function calculates the area and perimeter of the rectangle and displays the result on the screen. The function returns no value.

Can someone HELP?

thankx
Jul 26 '06 #1
2 3763
I am new in C++, and learning the langauge by my self only, while practicing i come across one question for which i have no idea, the question is to calculate area and perimeter of rectangle, the code i wrote was


#include <iostream>
using namespace std;
int main ()
{
// declaration of variables
float length; //length of a rectangle
float width; //width of a rectangle
float area; //area of a rectangle
float perim; //perimeter of a rectangle
// prompt for and read the input values
cout << "Enter the length of the rectangle" << endl;
cin >> length;
cout << "Enter the width of the rectangle" << endl;
cin >> width;
//Calculate the area and the perimeter
area = length*width;
perim = 2.0*length + 2.0*width;
//Display the result
cout << "The area is " << area << endl;
cout << "The perimeter is " << perim << endl;

return 0;

}

BUT I WHAT I NEED IS

The program will read the values of length and width from the user trough keyboard and passes these values to the function calculate(T x, T y). The function calculates the area and perimeter of the rectangle and displays the result on the screen. The function returns no value.

Can someone HELP?

thankx

Hi,
Your code is already doing the same what you need. The only thing is you want the calculation of perimeter to be done by another fuction called Calculate( ); so just cut copy paste the code inside the fuction Calculate( ); like

void Calculate(float Tx, float Ty)
{
float area;

area = (2*Tx) + (2*Ty);
"
"
"
}

But I dont think that u are asking this, if not then pls elobrate ur question.
Jul 26 '06 #2
Banfa
9,056 Expert Mod 8TB
Templates basically allow you to write functions or classes where the types of the variables are determined at compile time rather than when you write the source. You can define 2 things in a template, a type or a value.

For your case only a type is required

Expand|Select|Wrap|Line Numbers
  1. template<class CalcType> void Calculate(CalcType x, CalcType y)
  2. {
  3.     CalcType area;
  4.     CalcType perim;
  5.  
  6.     //Calculate the area and the perimeter
  7.     area = x*y;
  8.     perim = 2.0*x + 2.0*y;
  9.     //Display the result
  10.     cout << "The area is " << area << endl;
  11.     cout << "The perimeter is " << perim << endl;
  12. }
  13.  
This defines a function where the type used in the calculation is not set. The compiler will instanciate versions of the function for all the types that we need, so for the following code

Expand|Select|Wrap|Line Numbers
  1.     float fp_width = 5.3;
  2.     float fp_height = 7.1;
  3.  
  4.     int int_width = 3;
  5.     int int_height = 9;
  6.  
  7.     Calculate(fp_width, fp_height);
  8.  
  9.     Calculate(int_width, int_height);
  10.  
the compiler will instanciate the following 2 versions of calculate automatically

Expand|Select|Wrap|Line Numbers
  1. void Calculate(float x, float y)
  2. {
  3.     float area;
  4.     float perim;
  5.  
  6.     //Calculate the area and the perimeter
  7.     area = x*y;
  8.     perim = 2.0*x + 2.0*y;
  9.     //Display the result
  10.     cout << "The area is " << area << endl;
  11.     cout << "The perimeter is " << perim << endl;
  12. }
  13.  
  14. void Calculate(int x, int y)
  15. {
  16.     int area;
  17.     int perim;
  18.  
  19.     //Calculate the area and the perimeter
  20.     area = x*y;
  21.     perim = 2.0*x + 2.0*y;
  22.     //Display the result
  23.     cout << "The area is " << area << endl;
  24.     cout << "The perimeter is " << perim << endl;
  25. }
  26.  
note if I want to I can force the compiler to use a specific type when I call the function

[/code]
Calculate<long>(int_width, int_height);
[code]

in the above code although both the variables are of type int I have told the compiler to instanciate a function that uses the type long for it's parameters and variables. On a system where int is 2 bytes this clearly has the advantage of preventing maths overflow inside the Calculate function.


Although it is not clear fom this case sometimes it is necessary to manual instanciate a version of the function with specific TYPEs. This is possible, for instance

Expand|Select|Wrap|Line Numbers
  1. template<> void Calculate(char *x, char *y)
  2. {
  3.     cout << "It is not possible to calculate the area and perimiter of variables of type char * " << endl;
  4. }
  5.  
This link as a half decent tutorial

http://www.is.pku.edu.cn/~qzy/cpp/vc-stl/templates.htm
Jul 26 '06 #3

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