Function is not being called, instead junk values are being used. How do I call the function and fix the issue?

Question

I've tried to perform a simple binary/linear search but there's a problem with the output, I suspect the function isn't being called

A small portion of void main:

 void main()
 {  cout<<"Linear or Binary? (1/2)"<<endl;
      cin>>ch;
   switch(ch)
   {
       case '1': pos = linear();
               cout<<"Position: "<<pos;
               break;
       case '2': pos = binary();
               cout<<"Position: "<<pos;
               break;
       default: cout<<"error"<<endl;
    }
 } 

                                             //here is a function:
int linear()
{    
     int a, n, ar[n], posn;
     cout<<"Enter size of array and array"<<endl;
     cin>>n;

     for(int i =0; i<n; i++)
     {
         cin>>ar[i];
     }

     cout<<"enter element to be found"<<endl;
     cin>>a;

     for(int j=0; j<n; j++)
     {
         if(ar[j]==a)
         {
             posn= j+1;
         }
     }
     return posn;
}

The output is just garbage or junk. None of my couts are showing up, simply one random int junk value.

Answer 1

There are quite a few problems in your code:-

• Leaving the values of important varibles such as posn and n uninitialized...

  C++ invokes undefined behavior the time you try to access the value of a variable that is not initialized... And UB can be anything, so the garbage value is expected ...

  To prevent that from happening, initialize them before use...

   int a, n, posn = -1; cout<<"Enter size of array and array"<<endl; cin>>n;

• C++ does not have the feature of variable length arrays yet (Only in C99 and above...) and hence ar[n] is not possible (Though there are some compilers like Ideone which support it, but according to the standard, it is not possible), that is why we have got the advantages of a class called vector inside of the namespace std

  Note: #include <vector> before use...

   int linear() { int a, n, posn = -1; cout << "Enter size of array and array: " << endl; cin >> n; // Use vectors for dynamic arrays (or pointers if you want to stay old-school...) vector ar(n); for(auto i = 0; i < n; i++) cin>>ar[i]; cout << "Enter element to be found: " << endl; cin >> a; for(auto j = 0; j < n; j++) if(ar[j] == a) posn= j + 1; }