Range-based for loop in C++

Range-based for loop in C++ is added since C++ 11. It executes a for loop over a range. Used as a more readable equivalent to the traditional for loop operating over a range of values, such as all elements in a container.

for ( range_declaration : range_expression ) 
    loop_statement

Parameters :
range_declaration : 
a declaration of a named variable, whose type is the 
type of the element of the sequence represented by 
range_expression, or a reference to that type.
Often uses the auto specifier for automatic type 
deduction.

range_expression : 
any expression that represents a suitable sequence 
or a braced-init-list.

loop_statement : 
any statement, typically a compound statement, which
is the body of the loop.

C++ implementation : 

CPP

// Illustration of range-for loop
// using CPP code
#include <iostream>
#include <map>
#include <vector>

// Driver
int main()
{
    // Iterating over whole array
    std::vector<int> v = { 0, 1, 2, 3, 4, 5 };
    for (auto i : v)
        std::cout << i << ' ';

    std::cout << '\n';

    // the initializer may be a braced-init-list
    for (int n : { 0, 1, 2, 3, 4, 5 })
        std::cout << n << ' ';

    std::cout << '\n';

    // Iterating over array
    int a[] = { 0, 1, 2, 3, 4, 5 };
    for (int n : a)
        std::cout << n << ' ';

    std::cout << '\n';

    // Just running a loop for every array
    // element
    for (int n : a)
        std::cout << "In loop" << ' ';

    std::cout << '\n';

    // Printing string characters
    std::string str = "Geeks";
    for (char c : str)
        std::cout << c << ' ';

    std::cout << '\n';

    // Printing keys and values of a map
    std::map<int, int> MAP(
        { { 1, 1 }, { 2, 2 }, { 3, 3 } });
    for (auto i : MAP)
        std::cout << '{' << i.first << ", " << i.second
                  << "}\n";
}

Output:

0 1 2 3 4 5 
0 1 2 3 4 5 
0 1 2 3 4 5 
In loop In loop In loop In loop In loop In loop 
G e e k s 
{1, 1}
{2, 2}
{3, 3}

C++ 17 or higher: Range-based loops can also be used with maps like this: 

for (auto& [key, value]: myMap) {
    cout << key << " has value " << value << std::endl;
}

Here [key, value] works like elements of pair which can be directly accessed without specifying first or second keyword. 

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