Question

I don't know how to run this code on visual studios and I don't understand why the answer is 211111118. Please explain! Thank you!

CONSIDER THE FOLLOWING CODE:
void Question()
{
      string x = "12";
      mystery1(x);
      string str1 = "21";
      mystery2(str1);
      string str2 = "11";
      mystery2(str2);
      string str3 = "31";
      mystery2(str3);
      string str4 = "91";
      mystery2(str4);
      string str5 = "81";
      mystery1(str5);
      x = x + str1 + str2 + str3 + str4 + str5;
      cout << x;
}
////////////////////////////////////////////////////////////
void mystery1(string &a)
{
      int num = a.length();
      string temp;
      for (int i = 0 ; i < num ; i++)
      {
            temp = a.at(i) + temp;
      }
      a = temp;

}
////////////////////////////////////////////////////////////
void mystery2(string &b)
{
      int num = b.length();
      string temp ="";
      for (int i = 0; i < num; i++)
      {
            if(b.at(i) == '1')
            temp = temp + b.at(i);
      }
      b = temp;

}

Answer 1

FULL CODE

#include "stdafx.h"

#include <iostream>

using namespace std;

////////////////////////////////////////////////////////////

void mystery1(string &a)

{

int num = a.length();

string temp;

for (int i = 0 ; i < num ; i++)

{

temp = a.at(i) + temp;

}

a = temp;

}

////////////////////////////////////////////////////////////

void mystery2(string &b)

{

int num = b.length();

string temp ="";

for (int i = 0; i < num; i++)

{

if(b.at(i) == '1')

temp = temp + b.at(i);

}

b = temp;

}

void Question()

{

string x = "12";

mystery1(x);

string str1 = "21";

mystery2(str1);

string str2 = "11";

mystery2(str2);

string str3 = "31";

mystery2(str3);

string str4 = "91";

mystery2(str4);

string str5 = "81";

mystery1(str5);

x = x + str1 + str2 + str3 + str4 + str5;

cout << x;

}

int main() {

Question();

}

Explanation:

mystery1() function modifies the string passed to it as the argument to its reverse.

mystery2() function modifies the string passed to it as the argument such that it contains only 1's now.

Hence,

string x = "12";

mystery1(x); ------> x = "21"

string str1 = "21";

mystery2(str1); ------> str1= "1"

string str2 = "11";

mystery2(str2); ----> str2 = "11"

string str3 = "31";

mystery2(str3); ------> str3 = "1"

string str4 = "91";

mystery2(str4); -----> str4 = "1"

string str5 = "81";

mystery1(str5); ------> str5 = "18"

x = x + str1 + str2 + str3 + str4 + str5; -----> x = "21" + "1" + "11" + "1" + "1" + "18" = "211111118"

cout << x;