Question

Some languages support many modes of parameter passing. Provide 2 examples using two different programming languages which support the user of the programming language deciding which to use when creating their method.

(Programming Languages)

Answer 1

Answer.

Step 1

There are different ways in which parameter data can be passed into and out of methods or functions. Let us assume that a function B() is called from another function A(). In this case A is called the “caller function” and B is called the “called function”. Also, the arguments which A sends to B are called actual arguments and the parameters of B are called formal arguments.

Important methods of parameter passing :

1. Call by Value.
2. Call by reference.

Step 2

In C++,

Call by value

• In call by value, value of variable is passed during function call.
• And copy this value in another variable at function definition.
• In call by value the original value in calling function will never change after execution of function.

example.

#include<iostream>

using namespace std;

void swap (int a, int b) {

int temp=a;

a=b;

b=temp;

}

int main () {

int x, y;

cout<<"enter value of a and b:";

cin>>x>>y;

swap (x, y);

cout<<"\nafter swapping a = "<<a<<"and b = "<<b;

return 0;

}

Output:

Enter value of a and b:

4

5

After swapping a = 5 and b = 4

Call by reference

• In call by reference, reference is passed during function call.
• The formal arguments in the called function become aliases to the actual function call.
• In call by reference the original value in calling function will change after execution of function.

example.

#include<iostream>

using namespace std;

void swap (int &a, int &b) // It is the only difference from above program

{

int temp=a;

a=b;

b=temp;

}

int main () {

int a,b;

cout<<"Enter two numbers:";

cin>>a>>b;

swap (a, b);

cout<<"a="<<a<<"b="<<b;

return 0;

}

Output:

Enter value of a and b:

4

5

After swapping a = 5 and b = 4

Step 3

In JAVA,

Call by value

• Call by Value means calling a method with a parameter as value.
• Through this, the argument value is passed to the parameter.

example.

public class TestByValue{
   public static void main(String[] args){
      int a = 30;
      int b = 45;
      System.out.println("Before swapping, a = " + a + " and b = " + b);
      // Invoke the swap method
      swap(a, b);
      System.out.println("\n**Now, Before and After swapping values will be same here**:");
      System.out.println("After swapping, a = " + a + " and b is " + b);
   }
   public static void swap(int a, int b) {
      System.out.println("Before swapping(Inside), a = " + a + " b = " + b);
      // Swap n1 with n2
      int c = a;
      a = b;
      b = c;
      System.out.println("After swapping(Inside), a = " + a + " b = " + b);
   }
}

Output:

Before swapping, a = 10 and b = 15
Before swapping(Inside), a = 10 b = 15
After swapping(Inside), a = 15 b = 10
**Now, Before and After swapping values will be same here**:
After swapping, a = 10 and b is 15

Call by reference

• Call by Reference means calling a method with a parameter as a reference.
• Through this, the argument reference is passed to the parameter.

example.

public class TestByReference {
   public static void main(String[] args) {
      IntWrapper a = new IntWrapper(30);
      IntWrapper b = new IntWrapper(45);
      System.out.println("Before swapping, a = " + a.a + " and b = " + b.a);
      // Invoke the swap method
      swap(a, b);
      System.out.println("\n**Now, Before and After swapping values will be different here**:");
      System.out.println("After swapping, a = " + a.a + " and b is " + b.a);
   }
   public static void swap(IntWrapper a, IntWrapper b) {
      System.out.println("Before swapping(Inside), a = " + a.a + " b = " + b.a);
      // Swap n1 with n2
      IntWrapper c = new IntWrapper(a.a);
      a.a = b.a;
      b.a = c.a;
      System.out.println("After swapping(Inside), a = " + a.a + " b = " + b.a);
   }
}
class IntWrapper {
   public int a;
   public IntWrapper(int a){ this.a = a;}
}

Output:

Before swapping, a = 10 and b = 15
Before swapping(Inside), a = 10 b = 15
After swapping(Inside), a = 15 b = 10
**Now, Before and After swapping values will be different here**:
After swapping, a = 15 and b is 10

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