# Add 1 to number represented as array | Recursive Approach

Given an array which represents a number, add 1 to the array. Suppose an array contain elements [1, 2, 3, 4] then the array represents decimal number 1234 and hence adding 1 to this would result 1235. So new array will be [1, 2, 3, 5].

Examples:

```Input :  [1, 2, 3, 4]
Output : [1, 2, 3, 5]

Input :  [1, 2, 9, 9]
Output : [1, 3, 0, 0]

Input:  [9, 9, 9, 9]
Output: [1, 0, 0, 0, 0]
```

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

Approach :
1. Add 1 to the last element of the array, if it is less than 9.
2. If it is 9, then make it 0 and recurse for the remaining element of the array.

## C++

 `// C++ Program to add 1 to an array ` `// representing a number ` `#include ` `using` `namespace` `std; ` ` `  `// function to add one and print the array ` `void` `sum(``int` `arr[], ``int` `n) ` `{ ` `     `  ` ``int` `i = n; ` ` `  ` ``// if array element is less than 9, then ` ` ``// simply add 1 to this. ` ` ``if``(arr[i] < 9) ` ` ``{ ` `     ``arr[i] = arr[i] + 1; ` `     ``return``; ` ` ``} ` ` `  ` ``// if array element is greater than 9, ` ` ``// replace it with 0 and decrement i ` `    ``arr[i] = 0; ` `    ``i--; ` ` `  `    ``// recursive function ` `    ``sum(arr, i); ` `     `  `    ``// If 1 was appended at head ` `    ``// of array then, print it ` `    ``if``(arr[0] > 0) ` `        ``cout << arr[0] << ``", "``; ` ` `  `    ``// print the array elements  ` `    ``// after adding one ` `    ``for``(``int` `i = 1; i <= n; i++) ` `    ``{ ` `            ``cout << arr[i]; ` `             `  `            ``if``(i < n) ` `                ``cout << ``", "``; ` `    ``} ` `} ` ` `  `// driver code ` `int` `main() ` `{ ` `    ``// number of elements in array ` `    ``int` `n = 4; ` ` `  `    ``// array elements, index of array ` `    ``// should be 1 based, hence, 0 is ` `    ``// added here at arr[0] ` `    ``int` `arr[] = {0, 1, 9, 3, 9}; ` ` `  `    ``// function calling ` `    ``sum(arr, n); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java Program to add 1 to an array ` `// representing a number ` `import` `java.io.*; ` ` `  `public` `class` `GFG { ` ` `  `    ``// function to add one and print the array ` `    ``void` `sum(``int``[] arr, ``int` `n) ` `    ``{ ` `        ``int` `i = n; ` ` `  `        ``// if array element is less than 9, then ` `        ``// simply add 1 to this. ` `        ``if` `(arr[i] < ``9``) { ` `            ``arr[i] = arr[i] + ``1``; ` `            ``return``; ` `        ``} ` ` `  `        ``// if array element is greater than 9, ` `        ``// replace it with 0 and decrement i ` `        ``arr[i] = ``0``; ` `        ``i--; ` ` `  `        ``// recursive function ` `        ``sum(arr, i); ` ` `  `        ``// If 1 was appended at head ` `        ``// of array then, print it ` `        ``if` `(arr[``0``] > ``0``) ` `            ``System.out.print(arr[``0``] + ``", "``); ` ` `  `        ``// print the array elements ` `        ``// after adding one ` `        ``for` `(i = ``1``; i <= n; i++) { ` `            ``System.out.print(arr[i]); ` ` `  `            ``if` `(i < n) ` `                ``System.out.print(``", "``); ` `        ``} ` `    ``} ` ` `  `    ``// driver code ` `    ``static` `public` `void` `main(String[] args) ` `    ``{ ` `        ``GFG obj = ``new` `GFG(); ` `         `  `        ``// number of elements in array ` `        ``int` `n = ``4``; ` ` `  `        ``// array elements, index of array ` `        ``// should be 1 based, hence, 0 is ` `        ``// added here at arr[0] ` `        ``int``[] arr = { ``0``, ``1``, ``9``, ``3``, ``9` `}; ` ` `  `        ``// function calling ` `        ``obj.sum(arr, n); ` `    ``} ` `} ` ` `  `// This code is contributed by vt_m. `

## Python 3

 `# Pyhton 3 Program to add 1 to an ` `# array representing a number ` ` `  `# function to add one and print  ` `# the array ` `def` `sum``(arr, n): ` ` `  `    ``i ``=` `n ` `     `  `    ``# if array element is less than ` `    ``# 9, then simply add 1 to this. ` `    ``if``(arr[i] < ``9``): ` `     `  `        ``arr[i] ``=` `arr[i] ``+` `1` `        ``return` `     `  `    ``# if array element is greater ` `    ``# than 9, replace it with 0 ` `    ``# and decrement i ` `    ``arr[i] ``=` `0` `    ``i ``-``=` `1` `     `  `    ``# recursive function ` `    ``sum``(arr, i) ` `     `  `    ``# If 1 was appended at head ` `    ``# of array then, print it ` `    ``if``(arr[``0``] > ``0``): ` `        ``print``(arr[``0``], ``", "``, end``=``"") ` `         `  `    ``# print the array elements  ` `    ``# after adding one ` `    ``for` `i ``in` `range``(``1``, n``+``1``): ` `         `  `        ``print``(arr[i], end``=``"") ` `        ``if``(i < n): ` `            ``print``(``", "``, end``=``"") ` `     `  `# driver code ` `# number of elements in array ` `n ``=` `4` ` `  `# array elements, index of array ` `# should be 1 based, hence, 0 is ` `# added here at arr[0] ` `arr ``=` `[``0``, ``1``, ``9``, ``3``, ``9``] ` ` `  `# function calling ` `sum``(arr, n) ` ` `  `# This code is contributed by ` `# Smitha Semwal `

## C#

 `// C# Program to add 1 to an array ` `// representing a number ` `using` `System; ` ` `  `public` `class` `GFG { ` `     `  `    ``// function to add one and print the array ` `    ``void` `sum(``int` `[]arr, ``int` `n){ ` `         `  `    ``int` `i = n; ` ` `  `    ``// if array element is less than 9, then ` `    ``// simply add 1 to this. ` `    ``if``(arr[i] < 9) ` `    ``{ ` `      ``arr[i] = arr[i] + 1; ` `      ``return``; ` `    ``} ` ` `  `    ``// if array element is greater than 9, ` `    ``// replace it with 0 and decrement i ` `    ``arr[i] = 0; ` `    ``i--; ` ` `  `    ``// recursive function ` `    ``sum(arr, i); ` `     `  `    ``// If 1 was appended at head ` `    ``// of array then, print it ` `    ``if``(arr[0] > 0) ` `        ``Console.Write(arr[0] + ``", "``); ` ` `  `    ``// print the array elements  ` `    ``// after adding one ` `    ``for``( i = 1; i <= n; i++) ` `    ``{ ` `            ``Console.Write(arr[i]); ` `             `  `            ``if``(i < n) ` `                ``Console.Write(``", "``); ` `    ``} ` `} ` ` `  `    ``// driver code ` `    ``static` `public` `void` `Main () ` `    ``{ ` `      ``GFG obj =``new` `GFG(); ` `         `  `    ``// number of elements in array ` `    ``int` `n = 4; ` ` `  `    ``// array elements, index of array ` `    ``// should be 1 based, hence, 0 is ` `    ``// added here at arr[0] ` `    ``int` `[]arr = {0, 1, 9, 3, 9}; ` ` `  `    ``// function calling ` `    ``obj.sum(arr, n); ` `    ``} ` `} `

Output :

```1, 9, 4, 0
```

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Improved By : Smitha Dinesh Semwal

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