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

In this section, we will see an interesting question. Suppose a number is given. We need to increase this number by 1. This is a very simple task. But here, we will place the numbers as an array. Each digit of the number is placed as an element of the array. If the number is 512, then it will be stored as {5, 1, 2}. And we also have to use recursive method to increase the number. Let’s look at the algorithm to get a 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

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