Major Difference Between Call by Value and Call by Reference in C++

User-defined functions are a crucial feature in C++ that allows users to write advanced programs. In C++, YOU can pass arguments to a function either through Call by Value or through Call by Reference. In this tutorial, you learn about call by value and call by reference in C++ and understand these methods in detail.

What Are Parameters?

Parameters refer to the values that are declared inside the parentheses. It passes these values to the function, and a comma separates each parameter from the other parameter. For example, if there is a function for adding or subtracting two numbers, then that function must have two parameters. 

Here n1, n2 are the parameters that are passed to the function add().

These parameters are of two types.

Formal parameters: These are those parameters that are passed during the declaration/ definition of a function.

Actual parameters: These are those parameters that are passed while calling the function.

Now, you will learn about Call by Value and Call by Reference in C++.

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Call by Value Method

Call by Value is a method in which it passes the copies of actual parameters to the formal parameters inside the function. And as you know, it passes the copies, so even if there is any change in the values inside the function, it will not reflect that change in the actual values.

Here copies of the values num1 and num2 are being passed to n1 and n2. The actual parameters are num1, num2, and it passes the copies of the values to the function's formal parameters.

Call by Reference Method

Call by Reference is a method in which it passes the reference or address of the actual parameter to the function's formal parameters, which means if there is any change in the values inside the function, it reflects that change in the actual values.

Here &n1 and &n2 are the reference or addresses to num1 and num2, and that is why the change in the formal parameter will be reflected in the actual parameter. 

Now let’s have a look at an example.

In this example, you assigned the variable salary with the value of 27000. It passes the reference of the variable to the function increment. Inside the function, it increments the value by 5000, and the output at line 27 would be 32000.

Now, as you passed the reference of the value, it will reflect the changes made in the actual value. That means at line 36, the actual value will also get incremented to 32000.

This is the output of the above example, and you can see that the actual value of variable salary has also changed, i.e. salary before the increment.

Let’s have a look at another example.

In this example, the only change is that here you are passing the value through the Call by value method. You passed the copy of the actual parameter to the formal parameter of the function increment. Inside the function, the value is incremented by 5000.

Now, as you know, there is no change in the actual value in the Call by value method. So the value of the variable sal will not change at line 36, i.e. salary before the increment. And only the output at line 27, i.e. salary after increment, will change to 32000.

This is the output of the above example, and you can see there is no change in the actual value, i.e. 27000.

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Difference Between Call by Value and Call by Reference

That was all about Call by value and call by reference in C++ article.

Conclusion

After reading this tutorial on call by value and call by reference in C++, you would have understood about these two methods and how both of these methods work, along with some examples. You also learned the difference between call by value and call by reference methods.

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