Can someone please help me solve this question?

[cplusplusgs]

Hello I have received this question from my lecturer, however, he is unwilling to teach me how to solve this question. This quiz is long over, however, I just wish to know how to solve it using C++, hope someone could help me along.

Question:

Given a non-negative integer n, we wish to list down those missing digits in n and
display them in increasing order.
You are suppose to provide k sets of integers for testing where k must be at least 5
and maximum 10. Data validation is required for k.
The following shows some possible interactions and displays:
_______________________________________________
Enter number of sets for testing: 55
Enter number of sets for testing: 8
Enter number of sets for testing:
Enter number of sets for testing:

Enter integer 1: 87240
Missing digits: 1 3 5 6 9

Enter integer 2: 0
Missing digits: 1 2 3 4 5 6 7 8 9

etc..

---------------

Thank you

[Hengry]

What I wrote is only checking once. You can always just add for / while loop, and reset the array for multiple checks. There is probably a better way to write this program, and I am also intrigued how anyone else would write this. You mentioned that this was for a quiz, so I think my solution wouldn't be the way you would write it down.

#include <iostream>
#include <string>
using namespace std;

int main()
{   
    const int size = 10;
    string numbers[size] = { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9" };
    string myNumbers[size];
    string numberString = "";
    cout << "Enter number for testing: ";
    cin >> numberString;
    // Place number inside an array
    for(int i = 0; i < numberString.length(); i++){
        myNumbers[i] = numberString.substr(i,1);    
    }
    // Compare the numbers with your numbers
    for(int i = 0; i < size; i++){
        for(int j = 0; j < numberString.length(); j++){
            // Sets equivalent numbers as "-1"
            if(numbers[i] == myNumbers[j]){
                numbers[i] = "-1";    
            }
        }
    }
    // Prints out all numbers that aren't -1
    for(int i = 0; i < size; i++){
        if(numbers[i] != "-1"){
         cout << numbers[i] << " ";
        }
    }
}

[cplusplusgs]

Thank you very much for helping! I really appreciate it! :)

[keskiverto]

I am also intrigued how anyone else would write this

Lets see what you do:

FOR EACH digit in [0..9]
  IF input CONTAINS digit
  THEN disable digit

FOR EACH digit in [0..9]
  IF digit IS enabled
  THEN PRINT digit

Do note that if input if 555, then the
IF 555 CONTAINS 5 (which you have on lines 19--24)
will on first iteration change the digit into -1
and on the other two iterations you will compare "-1" with "5".
There is no need to do those two iterations; we already know that input contains at least one 5.
There is statement break that helps us to cut the loop short.

There is a shorter path too:

FOR EACH digit in [0..9]
  IF input DOES NOT CONTAIN digit
  THEN PRINT digit

Implementation-wise do note that a std::string has an array of characters and a digit is a single character. You treat digits as strings (probably to accomodate the "-1"). You use arrays of strings.
Less is more.

std::string has member function find(). You can use it for the CONTAINS test.
Library has std::find(), if you want to operate with arrays (or containers).

[48T7M4Gy]

#include <iostream>

int main()
{
    int digit[10]{0};
    int number{0};
    
    std::cout << "Please enter an integer: ";
    std::cin >> number;
    
    if(number != 0)
    {
        while(number > 0)
        {
            digit[number % 10]++;
            number /= 10;
        }
    }
    else
        digit[0] = 1;
    
    for(int i = 0; i < 10; ++i)
    {
        if(digit[i] == 0)
            std::cout << i << ' ';
    }
    std::cout << '\n';
    
    return 0;
}

[Enoizat]

So simple and effective, kemort! I worked out a solution based on std::strings, but it looks so stupid compared with yours...

[cplusplusgs]

Thank you Keskiverto, Kemort and also Enoizat! :)

[lastchance]

#include <iostream>
#include <string>
using namespace std;

int main()
{
   bool used[10] = { 0 };
   string input;
   cout << "Enter a positive integer: ";
   cin >> input;
   for ( char c : input ) used[c-'0'] = true;
   for ( int i = 0; i < 10; i++ ) if ( !used[i] ) cout << i << " ";
}

Enter a positive integer: 87240
1 3 5 6 9