# Sum of odd is square

## Art of Code 01

Today, i write a simple program that prints squares in numbers, to prove that the sum of odd numbers are square.

If we have one item and add a odd number of items to it, the items forms a square.

• 2 Square = 4 = 1 + 3
• 4 Square = 16 = 1+3+5+7
• n Square = 1 + odd numbers

The Output of `aoc_01-sumofofodd.cpp`

``````1
4
9
16
25
36
49
64
81
``````

A geometrical Prove of the sum of Odd is square: ### appendix std::vector, auto and const

`std::vector` - Vectors

``````    vector<int> v = {1, 4, 2};
``````

`auto`, explicit declared is so nineties ;-)

In “modern” c++, the compiler can decide which type applies.

``````    auto v = {1, 4, 2};
for (auto i: v)
cout << i << "\n";
``````

We may also explicit tell the compiler we read only with `const`:

``````    auto v = {1, 4, 2};
for (const int &i: v)
cout << i << "\n";
``````

### aoc_01-sumofofodd.cpp

To compile and play with the sum of odds in C++:
`g++ aoc_01-sumofofodd.cpp && ./a.out`
or
`clang++ -std=c++11 -stdlib=libc++ -g aoc_01-sumofofodd.cpp && ./a.out`

Written on August 8, 2020