C++

Premise

To be more exact, we should include all the needed headers first.

For example:

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#include <iostream> // for I/O
#include <iterator> // for istream_iterator
#include <vector> // for vector
#include <string> // for string

Actually, since we are usually hosted on machines with GCC, we can include only:

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#include <bits/stdc++.h>

Which makes everything from the STL available. Remember this header is not standard.

Reading an array of N elements

The first line contains N, the number of elements.

The next line contains N space-separated integers.

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int N;
std::cin >> N;
std::vector<int> v(N);
std::copy_n(std::istream_iterator<int>(std::cin), N, begin(v));

Using copy_n is the best choice because we can use it to read more things in sequence:

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int N1, N2;
std::cin >> N1 >> N2;
std::vector<int> v1(N1);
std::vector<int> v2(N2);
std::copy_n(std::istream_iterator<int>(std::cin), N1, begin(v1));
std::copy_n(std::istream_iterator<int>(std::cin), N2, begin(v2));

Reading strings

We can simply use std::string:

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std::string s;
std::cin >> s;

If the string length is introduced first, we can either read it:

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int N;
std::cin >> N; // not used
std::string s;
std::cin >> s;

or ignore it (there are many ways, here is the simplest):

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std::string s;
std::cin >> s >> s;

Output

We can easily print values and strings by sending them to cout:

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std::cout << value << " " << stringValue << "\n";

Printing arrays

Vectors and arrays are easy to std::copy to standard output.

If v is a vector or array of ints, we can print its content separated by whitespaces this way:

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std::copy(begin(v), end(v), std::ostream_iterator<int>(std::cout, " "));

If we must omit the last whitespace, we can do the following refinement:

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std::copy(begin(v), std::prev(end(v)), std::ostream_iterator<int>(std::cout, " "));
std::cout << *std::prev(end(v));

Floating point with exact precision

Some challenges require printing floting points with a certain width.

In such cases, we use std::fixed in combination with std::setprecision(numberOfDigits) can be used.

For instance, suppose we want only two digits after comma:

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cout << fixed << setprecision(2) << value << "\n";

Or suppose we want only one digit after comma:

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cout << fixed << setprecision(1) << value << "\n";