# C++ Revision Day-3

### 1) **What is the difference between reference and pointer?**

| Reference | Pointer |
| --- | --- |
| Reference is used to refer to an existing variable in another name. | Pointers are used to store the address of a variable. |
| References cannot have a null value assigned | The pointer can have a null value assigned |
| A reference variable can be referenced by passing by the value | The pointer can be referenced but passed by reference |
| A reference must be initialized on the declaration | Pointers needs no initialization on the declaration |
| A reference shares the same memory address with the original variable and takes up some space on the stack | Pointer has its own memory address and size on the stack |

2. **What is STL in C++ with an example?**
    

[STL in C++](https://www.mygreatlearning.com/blog/standard-template-library-in-c/) is a library and abbreviation of Standard Template Library. STL is a generalized library that provides common programming data structures/ container classes, functions, algorithms, and iterators. STL has four components

```plaintext
- Algorithms: Searching and sorting algorithms such as binary search,
  merge sort etc.

- Containers: Vector, list, queue, arrays, map etc.

- Functions: They are objects that act like functions.

- Iterators: It is an object that allows transversing through elements 
  of a container, e.g., vector<int>::iterator.
```

### 3) **What is an inline function in C++?**

[Inline functions](https://www.mygreatlearning.com/blog/inline-functions-in-cpp/) are used to increase the execution time of a program. If a function is inline, the compiler puts the function code wherever the function is used during compile time. The syntax for the same is as follows:

### 4) **What is friend function in C++?**

A friend function has access rights to all private and protected members of the class.

```cpp
class Circle
    {   
    double radius;   
    public:      
    friend void printradius( Circle c );  
    };
void printradius(Circle c ) 
    {   
    /* Because printradius() is a friend of Circle, it can
        directly access any member of this class */   
    cout << "Radius of circle: " << c.radius;
    }
int main() 
    {   
    Circle c;   
    // Use friend function to print the radius.   
    printradius( c);   
    return 0;
    }
```