how to extract digits beginning from the first digit ?

Answer 1

Here's a little program to treat an integer like an array. You can get the digit at its index (zero based).

#include <iostream>
#include <stdexcept>
#include <sstream>

using namespace std;

int getNumberOfDigits(int number) {
int length = 1;

while((number /= 10) != 0){
++length;
}

return length;
}

int getDigitAtIndex(int number, int index) {
int numAtIndex = 0;
int count = getNumberOfDigits(number) - index;

if(index < 0 || count <= 0) {
stringstream str;
str << "Index of " << index << " is out of range";
throw out_of_range(str.str());
}

for(int i = count; i > 0; --i) {
numAtIndex = number % 10;
number /= 10;
}

return numAtIndex;
}

int main() {
int number = 12345;
cout << getDigitAtIndex(number, 0);
return 0;
}

Answer 2

The striaght-forward/naive way would be keep dividing the integer by 10 and get the last non-zero quotient.

567 ÷ 10 = 56
56 ÷ 10 = 5 ⬅
5 ÷ 10 = 0

Answer 3

yep as he ☝said for getting from back
a[ i ]=n%10;
n/10;

or to get from front
while(size){
a[ i ] = n/exp(10, --size);
n-=exp(10,size+1);}

here size is no. of digits in n