#include <string>
#include <iostream>
#include <variant>

struct SampleVisitor
{
    void operator()(int i) const { 
        std::cout << "int: " << i << "\n"; 
    }
    void operator()(float f) const { 
        std::cout << "float: " << f << "\n"; 
    }
    void operator()(const std::string& s) const { 
        std::cout << "string: " << s << "\n"; 
    }
};

int main()
{
    std::variant<int, float, std::string> intFloatString;
    static_assert(std::variant_size_v<decltype(intFloatString)> == 3);

    // default initialized to the first alternative, should be 0
    std::visit(SampleVisitor{}, intFloatString);

    // index will show the currently used 'type'
    std::cout << "index = " << intFloatString.index() << std::endl;
    intFloatString = 100.0f;
    std::cout << "index = " << intFloatString.index() << std::endl;
    intFloatString = "hello super world";
    std::cout << "index = " << intFloatString.index() << std::endl;

    // try with get_if:
    if (const auto intPtr (std::get_if<int>(&intFloatString)); intPtr) 
        std::cout << "int!" << *intPtr << "\n";
    else if (const auto floatPtr (std::get_if<float>(&intFloatString)); floatPtr) 
        std::cout << "float!" << *floatPtr << "\n";

    if (std::holds_alternative<int>(intFloatString))
        std::cout << "the variant holds an int!\n";
    else if (std::holds_alternative<float>(intFloatString))
        std::cout << "the variant holds a float\n";
    else if (std::holds_alternative<std::string>(intFloatString))
        std::cout << "the variant holds a string\n";  

    // try/catch and bad_variant_access
    try 
    {
        auto f = std::get<float>(intFloatString); 
        std::cout << "float! " << f << "\n";
    }
    catch (std::bad_variant_access&) 
    {
        std::cout << "our variant doesn't hold float at this moment...\n";
    }

    // visit:
    std::visit(SampleVisitor{}, intFloatString);
    intFloatString = 10;
    std::visit(SampleVisitor{}, intFloatString);
    intFloatString = 10.0f;
    std::visit(SampleVisitor{}, intFloatString);
}

C++ Online Compiler

Write, Run & Share C++ code online using OneCompiler's C++ online compiler for free. It's one of the robust, feature-rich online compilers for C++ language, running on the latest version 17. Getting started with the OneCompiler's C++ compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as C++ and start coding!

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
}