# Print Number series without using any loop

Problem – Givens Two number N and K, our task is to subtract a number K from N until number(N) is greater than zero, once the N becomes negative or zero then we start adding K until that number become the original number(N).
Note : Not allow to use any loop.

Examples :

```Input : N = 15 K = 5
Output : 15 10 5 0 1 5 10 15

Input : N = 20 K = 6
Output : 20 14 8 2 -4 2 8 14 20
```

Explanation – We can do it using recursion idea is that we call the function again and again until N is greater than zero (in every function call we subtract N by K). Once the number becomes negative or zero we start adding K in every function call until the number becomes the original number. Here we use a single function for both addition and subtraction but to switch between addition or subtraction function we used a Boolean flag.

Code –

`// C++ program to Print Number`
`// series without using loop`
`#include <iostream>`
`using` `namespace` `std;`
`// function print series`
`// using recursion`
`void` `PrintNumber(``int` `N, ``int` `Original, ``int` `K, ``bool` `flag)`
`{`
`    ``// print the number`
`    ``cout << N << ``" "``;`
`    ``// change flag if number`
`    ``// become negative`
`    ``if` `(N <= 0)`
`        ``flag = !flag;`
`    ``// base condition for`
`    ``// second_case (Adding K)`
`    ``if` `(N == Original && !flag)`
`        ``return``;`
`    ``// if flag is true`
`    ``// we subtract value until`
`    ``// number is greater then zero`
`    ``if` `(flag == ``true``) {`
`        ``PrintNumber(N - K, Original, K, flag);`
`        ``return``;`
`    ``}`
`    ``// second case (Addition )`
`    ``if` `(!flag) {`
`        ``PrintNumber(N + K, Original, K, flag);`
`        ``return``;`
`    ``}`
`}`
`// driver program`
`int` `main()`
`{`
`    ``int` `N = 20, K = 6;`
`    ``PrintNumber(N, N, K, ``true``);`
`    ``return` `0;`
`}`

Output :

```20 14 8 2 -4 2 8 14 20

```

Disclaimer: This does not belong to TechCodeBit, its an article taken from the below
source and credits.
source and credits:http://www.geeksforgeeks.org/print-number-series-without-using-loop/
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rakesh