Reference Passing

Reference passing allows variable to be modified by the function it's passed to.

Passing By Value

Let's look at the following example:

#include <iostream> using namespace std; void incrementValue(int num) { num++; } int main() { int num = 0; incrementValue(num); cout << num; }

Output:

0

num is incremented by 1 in theincrementValue function. Since it's passed by value it remains 0 in the main function.

Passing By Reference

To pass by reference, the symbol & needs to be added before argument's name:

#include <iostream> using namespace std; void incrementValue(int &num) { num++; } int main() { int num = 0; incrementValue(num); cout << num; }

Output:

1

Since num is passed by reference at line 5, it's value has incremented inside the main function too.

Array Arguments

Arrays are always passed by reference.

#include <iostream> using namespace std; void modifyArray(int arrayArg[]) { arrayArg[0] = 3; arrayArg[1] = 4; } int main() { int arr[2] = { 1, 2 }; modifyArray(arr); cout << arr[0] << " " << arr[1]; }

Output:

3 4

Though not specified via the & symbol, array still gets modified by the function it's passed to.