# [[Pass by Reference]]
- Formal parameter is a pointer
- Actual parameter is a pointer or address of variable
```cpp
void double_data(int *int_ptr);
void double_data(int *int_ptr) {
*int_ptr *= 2;
}
```
- Function parameter is pointer to integer
- Function call expects address to integer
```cpp
int main() {
int value {10};
cout << value << endl; // 10
double_data(&value);
cout << value << endl; // 20
}
```