# C Program to 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
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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.

 `// C++ program to Print Number ` `// series without using loop ` `#include ` ` `  `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
```

Please refer complete article on Print Number series without using any loop for more details!

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