Question

Lab 6.6

–

Using Value and Reference Parameters

Below is a copy of the source code.

1 // Lab 6 swapNums.cpp --

Using Value and Reference Parameters

2 // This program uses a function to swap the values in two variables

.

3 // PUT YOUR NAME HERE.

4 #include <iostream>

5 using namespace std;

6

7 // Function prototype

8 void swapNums(int, int);

9

10 /***** main *****/

11 int main()

12 {

13 int num1 = 5,

14 num2 = 7;

15

16 // Print the two

variable values

17 cout << "In main the two numbers are "

18 << num1 << " and " << num2 << endl;

19

20 // Call a function to swap the values stored

21 // in the two variables

22 swapNums(num1, num2);

23

24 // Print the same two variable values again

25 cout << "Back in main again the two numbers are "

26 << num1 << " and " << num2 << endl;

27

28 return 0;

29 }

30

31 /***** swapNums *****/

32 void swapNums(int a, int b)

33 { // Parameter a receives num1 and parameter b receives num2

34 // Swap the values that came into parameters a and b

35 int temp = a;

36 a = b;

37 b = temp;

38

39 // Print the swapped values

40 cout << "In swapNums, after swapping, the two numbers are "

41 << a << " and " << b << endl;

42 }

The question I need an answer for is:

Step 3:

Change the two swapNums parameters to be reference variables. Section 6.13 of your text shows how to do this. You will need to make the change on both the function header and the function prototype. Nothing will need to change in the function call. After making this change, recompile and rerun the program. If you have done this correctly, you should get the following output.

In main the two numbers are 5 and 7

In swapNums, after swapping, the two numbers are 7 and 5

Back in main again the two numbers are 7 and 5

Explain what happened this time. _______________________________________________________

Answer 1

Modified C++ Program

// PUT YOUR NAME HERE. #include <iostream> using namespace std; // Function prototype void swapNums(int &, int &); /***** main *****/ int main() { int num1 = 5, num2 = 7; // Print the two variable values cout << "In main the two numbers are " << num1 << " and " << num2 << endl; // Call a function to swap the values stored // in the two variables swapNums(num1, num2); // Print the same two variable values again cout << "Back in main again the two numbers are " << num1 << " and " << num2 << endl; return 0; } /***** swapNums *****/ void swapNums(int &a, int &b) { // Parameter a receives num1 and parameter b receives num2 // Swap the values that came into parameters a and b int temp = a; a = b; b = temp; // Print the swapped values cout << "In swapNums, after swapping, the two numbers are " << a << " and " << b << endl; }

OUTPUT

Explanation

When we are using reference parameters, then we are passing the memory address of the variables num1 and num2 declared in main. Hence in the function body when numbers are swapped then the process is directly reflected to the original memory address of the variables declared in main. As a result numbers are swapped in the function affecting the original variables in main.