Second Largest Digit in a number

[user1994]

Hi.! I am a beginner in c++. i came across a question where you have to find out the second largest digit in a given number.

Such as :

(1) Input : 8735 Output : 7 (Second Largest)
(2) Input : 3377 Output : 3 (Second Largest)

I have applied the logic below but it's not working. Can anyone suggest any idea

  for(int n : c)
        {
            if(l<n)
            {
                secondlargest = l;
                largest = n;
            }
            else
                if(n < largest && n > secondlargest )
                {
                    secondlargest = n;
                }
        }

[Shira]

who is it 'n'? and who is it 'c'?

[Shira]

What is this writing of the 'for'?
Are you sure that is correct in C++?

[andywestken]

@Shira

for(int n : c)

is valid in C++11 if c is a container -- it's a range-based for loop.

Andy

C++11 range-based for loops
http://www.cprogramming.com/c++11/c++11-ranged-for-loop.html

[cire]

What is this writing of the 'for'?
Are you sure that is correct in C++?

Yes, provided c is of a type for which begin(c)/end(c) are appropriately defined.

To the OP: What is l and why does it make sense to you to execute line 3 for every iteration of the loop?

[user1994]

@cire

I am sorry l is largest... I used different variables in my codeblocks...

Refined code :

for(int n : c)
        {
            if(l<n)
            {
                secondlargest = largest;
                largest = n;
            }
            else
                if(n < largest && n > secondlargest )
                {
                    secondlargest = n;
                }
        }

[keskiverto]

How should you handle:
(1) Input : 3
(2) Input : 666
(3) Input : -17

[user1994]

@keskiverto

That is the issue i am facing... I tried another logic by storing the digits in the array and printing the second largest integer by printing out the value of the second last element of the array :

Input : 9625
Output : 5

But the problem now is :

Input : 2299
Output: should be 2 but is 9 (obviously because sorted array will have 9 as the second last element).

How do i remove digits from array which are the same ? (As in i have to remove one 2 and one 9 in the above case)

[mutexe]

look at std::set and stuff like that.
you can make it so your collection adds only unique numbers.
I'm not on my machine at the moment so i can't give you an example, but have a google of the emplace method. (once you've determined a character is actually a number).
http://www.cplusplus.com/reference/set/set/emplace/

[cire]

http://en.cppreference.com/w/cpp/algorithm/unique

[andywestken]

As this is a beginner's exercise I would have thought resorting to the standard algorithms and containers would be cheating? Also, I don't see a need for storing more values than largest and secondlargest.

Consider what should happen when n == largest !!

Andy

PS You could go back an finish fixing your "refined" code!

EDIT

Actually, if I fix your code (l -> largest) it does give 2 for the second largest digit in 2299, not 9 ??

#include <iostream>
using namespace std;

void test(int value);

int main ()
{
    test(1234);
    test(8735);
    test(3377);   
    test(2299);

    return 0;
}

void test(int value)
{
    int c[16] = {0};

    cout << "value = " << value << "\n";
    cout << "\n";

    int count = 0;
    while(0 < value) {
        c[count++] = value % 10;
        value /= 10;
    }

    int largest = 0;
    int secondlargest = 0;

    for(int n : c)
    {
        if(largest<n)
        {
            secondlargest = largest;
            largest = n;
        }
        else
            if(n < largest && n > secondlargest )
            {
                secondlargest = n;
            }
    }

    cout << "largest        = " << largest       << "\n";
    cout << "second largest = " << secondlargest << "\n";
    cout << "\n";
}

C++ Shell output:

value = 1234

largest        = 4
second largest = 3

value = 8735

largest        = 8
second largest = 7

value = 3377

largest        = 7
second largest = 3

value = 2299

largest        = 9
second largest = 2

[cire]

As this is a beginner's exercise I would have thought resorting to the standard algorithms and containers would be cheating? Also, I don't see a need for storing more values than largest and secondlargest.

Such things can serve as inspiration. As to the second, the OP mentioned he was already dealing with a sorted array; std::unique (or equivalent code by the OP) seemed only natural.