#include <iostream>
#include <cstdlib>
#include <memory>
#include <vector>
#include <cstring>

class MyClass {
public:
    MyClass() { std::cout << "MyClass constructed\n"; }
    ~MyClass() { std::cout << "MyClass destructed\n"; }
};

int main() {
    // 1. new and delete operators
    std::cout << "1. new and delete operators:\n";
    MyClass* ptr = new MyClass();
    delete ptr;

    int* arr = new int[5];
    delete[] arr;

    // 2. C-style memory management
    std::cout << "\n2. C-style memory management:\n";
    int* c_ptr = (int*)malloc(sizeof(int));
    *c_ptr = 10;
    std::cout << "malloc: " << *c_ptr << std::endl;
    free(c_ptr);

    int* c_arr = (int*)calloc(5, sizeof(int));
    std::cout << "calloc: " << c_arr[0] << std::endl;  // Will be 0
    c_arr = (int*)realloc(c_arr, 10 * sizeof(int));
    free(c_arr);
    
    // memset with integers (be cautious!)
    int numbers[5] = {1, 2, 3, 4, 5};
    std::cout << "\nBefore memset: ";
    for (int i = 0; i < 5; ++i) std::cout << numbers[i] << " ";
    std::cout << std::endl;
    
    memset(numbers, 0, sizeof(numbers));
    std::cout << "After memset:  ";
    for (int i = 0; i < 5; ++i) std::cout << numbers[i] << " ";
    std::cout << std::endl;
    
    std::cout << "\nmemcpy example:\n";
    char srcMemCpy[] = "Hello, memcpy!";
    char destMemCpy[20];
    
    memcpy(destMemCpy, srcMemCpy, strlen(srcMemCpy) + 1);  // +1 to include null terminator
    std::cout << "Source: " << srcMemCpy << std::endl;
    std::cout << "Destination: " << destMemCpy << std::endl;

    // 3. Smart Pointers
    std::cout << "\n3. Smart Pointers:\n";
    std::unique_ptr<MyClass> uptr = std::make_unique<MyClass>();
    std::shared_ptr<MyClass> sptr = std::make_shared<MyClass>();
    std::weak_ptr<MyClass> wptr = sptr;

    // 4. Allocator
    std::cout << "\n4. Allocator:\n";
    std::allocator<int> alloc;
    int* alloc_ptr = alloc.allocate(1);
    alloc.construct(alloc_ptr, 42);
    std::cout << "Allocator: " << *alloc_ptr << std::endl;
    alloc.destroy(alloc_ptr);
    alloc.deallocate(alloc_ptr, 1);

    // 5. Other memory-related functions
    std::cout << "\n5. Other memory-related functions:\n";
    int x = 10;
    int* addr = std::addressof(x);
    std::cout << "addressof: " << addr << std::endl;

    std::vector<int> src = {1, 2, 3, 4, 5};
    std::vector<int> dest(5);
    std::uninitialized_copy(src.begin(), src.end(), dest.begin());
    std::cout << "uninitialized_copy: " << dest[2] << std::endl;

    // 6. C++17 std::launder (usage is advanced and situational)
    // Example omitted due to its specialized nature

    // 7. C++20 additions
    #if __cplusplus >= 202002L
    std::cout << "\n7. C++20 additions:\n";
    auto uptr_overwrite = std::make_unique_for_overwrite<int>();
    auto sptr_overwrite = std::make_shared_for_overwrite<int>();
    #endif

    // 8. Placement new
    std::cout << "\n8. Placement new:\n";
    char memory[sizeof(MyClass)];
    MyClass* placed_ptr = new (memory) MyClass();
    placed_ptr->~MyClass();  // Call destructor manually

    return 0;
}
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Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

#include <iostream>
#include <string>
using namespace std;

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}