My Program Works but Im not sure why!

[sideways]

Hello I am new to the forum, I am teaching myself C++ using the book "Programming Principles and Practice Using C++". I am doing one of the drills were you are asked to create a program that reads in ints and then displays them, states which has the greatest value and which has the least value. That is the easy part. The part I am having trouble with is stating when two of the integers entered are equal.

I got the program to work by using a while loop and an if statement, however I am not sure why this is need. I kind of just took a shot in the dark and it worked, I am not sure why the first while loop is needed, it seems a little repetitive to me.

Any help would be appreciated.

 
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>

using namespace std;

inline void keep_window_open(){ char ch; cin >> ch;}

int main(){

     vector <int> numbers;
     int previous;
     int x;
    
 while (cin >> x){

     if ( x != previous)
          numbers.push_back(x);

     else if (x == previous)
          previous = x;
}

int a;
std :: sort (numbers.begin(), numbers.end());

for (int a : numbers)
     cout << a << '\n';
     cout <<"Smallest Number is " << numbers[0] << '\n';
     cout << "Largest Number is " << numbers[numbers.size()-1]<<'\n';

for (int i; i < numbers.size(); ++i)
     if (numbers[i] == numbers[i+1])
     cout << "This number is repeated " << numbers[i];

return 0;
}
     

[sideways]

Never mind, I tried a different compiler and it seems to work without the if statement in the first while loop. I'm not sure why my compiler was giving me trouble.

[xismn]

If I'm understanding you correctly, the vector of numbers shouldn't contain any duplicate numbers. Each element is supposed to be unique. Is this correct?

There are some problems with your solution:

1.) You access the variable previous on lines 19 and 22, but you haven't initialized it. The variable contains garbage. This is only really a problem until you assign a value to it on line 23, but a problem nonetheless.

2.) The previous variable only keeps track of the last number entered. This means that a user could input the sequence 1, 2, 1, effectively pushing duplicate numbers onto the vector. This isn't really a huge concern, since the vector will be sorted, and duplicate values will not affect your final results, but unless that is explicitly what you had in mind, it is a flaw in your design.

EDIT - just took a closer look at your code. Obviously, it's not a concern if there exist duplicates. Your for loop on lines 34-36, however, assumes the vector is sorted, which is a bit iffy. It also deserves some opening and closing braces. Additionally, if I enter the sequence 1, 1, 1, your program will state that "1" is repeated twice - not that the number exists twice in the vector, but it will literally print the same message twice.

3.) On line 34, your integer i hasn't been initialized. It contains garbage. You then use i as an index for every iteration of the loop. You also access it in the for loop's condition, and increment garbage + 1 for every iteration.

[sideways]

Awesome thanks for the help! I haven't been initializing my ints because my compiler lets me get away with it, but your right I should be more thorough.