# Adding one to number represented as array of digits in C Program?

In this section we will see one interesting problem. Suppose one number is given. We have to increase this number by 1. This is extremely simple task. But here we will place the number as an array. each digit of that number is placed as an element of the array. If the number is 512, then it will be stored as {5, 1, 2}. And also we have to increase the number using recursive approach. Let us see the algorithm to get the clear idea.

## Algorithm

increment(arr, n, index) −

Initially the default value of index is 0
begin
if index < n, then
if arr[index] < 9, then
arr[index] := arr[index] + 1
else
arr[index] := 0
increment(arr, n, index + 1)
end if
if index = n, then
arr[n] := 1
n := n + 1
end if
end

## Example

#include <iostream>
#include <cmath>
#define MAX 20
using namespace std;
void increment(int num_arr[], int &n, int index = 0){
if(index < n){
if(num_arr[index] < 9){ //if digit is less than 9, add 1
num_arr[index]++;
}else{ //otherwise increase number recursively
num_arr[index] = 0;
increment(num_arr, n, index+1);
}
}
if(index == n){
num_arr[n] = 1; //add extra carry
n++; //increase n
}
}
void dispNumber(int num_arr[], int n){
for(int i = n-1; i>= 0; i--){
cout << num_arr[i];
}
cout << endl;
}
int numToArr(int num_arr[], int number){
int i = 0;
int n = log10(number) + 1;
for(int i = i; i< n; i++){
num_arr[i] = number % 10;
number /= 10;
}
return n;
}
main() {
int number = 1782698599;
int num_arr[MAX];
int n = numToArr(num_arr, number);
cout << "Initial Number: "; dispNumber(num_arr, n);
increment(num_arr, n);
cout << "Final Number: "; dispNumber(num_arr, n);
}

## Output

Initial Number: 1782698599
Final Number: 1782698600