How to determine the tens digit of a number in C++

Question

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How to get the digits of a number without converting it to a string/ char array?

I am stuck doing this task in C++; what I want to do is to figure out the the units digit and the tens digits of any number given by the user.

For example, if the number is 9775, the units digit is obtained as 9775 % 10, but I am stuck finding the tens digit.

Change the tens digit to be the units digit (by dividing by ten). You know how to get the units digit. — Peter Wood, Oct 09 '12 at 07:57

score 15 · Accepted Answer · answered Oct 09 '12 at 07:50

15

For a non-negative integer x the tens digit is (x / 10) % 10.

answered Oct 09 '12 at 07:50

arx

16,686
2
44
61

What? How? 18/10 = 1.8, 1.8%10 = 1.8 – Parijat Kalia Dec 02 '15 at 20:53
2

@ParijatKalia The question is about C++. My answer is about C++. My answer is also true for maths in general. But it isn't true for Javascript. – arx Dec 03 '15 at 15:12
@ParijatKalia 18/10 = 1 in C, and modding it by 10 will give you 1. So it actually is 1. Older computers did division weird – Shah Jacob Mar 31 '22 at 21:28

score 4 · Answer 2 · edited Dec 11 '18 at 15:01

4

#include <math.h>

int getdigit(int number, int digit)
{
   return (number / ((int) pow(10, digit)) % 10);
}

Where the first digit is 0. I don't really like floating point numbers getting involved (via pow), though.

edited Dec 11 '18 at 15:01

Rivasa

6,510
3
35
64

answered Oct 09 '12 at 08:02

LubosD

781
6
18

PiotrNycz · Answer 3 · 2012-10-09T15:20:16.383

Try to use very rarely used functions:

http://www.cplusplus.com/reference/clibrary/cstdlib/div/

 div_t div (           int numer,           int denom );
 ldiv_t div (      long int numer,      long int denom );  // C++ only
lldiv_t div ( long long int numer, long long int denom );  // C++11 only

E.g. with a simple loop:

std::vector<int> getDigits(unsigned int numer)
{
  std::deque<int> rv;
  do {
     div_t res = div(numer, 10);
     rv.push_front(res.rem);
     numer = res.quot;
  } while (numer > 0);
  return std::vector<int>(rv.begin(), rv.end());  
}

How to determine the tens digit of a number in C++

3 Answers3