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#include <iostream>

using namespace std;

double vals[] = {10.1, 12.6, 33.1, 24.1, 50.0};

double& setValues(int i) {  
   double& ref = vals[i];    
   return ref;   // Returns a reference to the i-th element, ref is a reference variable, ref refers to vals[i]
}

// Main function to call the above defined function
int main ()
{
   cout << "Values before change" << endl;
   for ( int i = 0; i < 5; i++ )
   {
       cout << "vals[" << i << "] = ";
       cout << vals[i] << endl;
   }

   setValues(1) = 20.23; // Changes the 2nd element
   setValues(3) = 70.8;  // Changes the 4th element

   cout << "Values after change" << endl;
   for ( int i = 0; i < 5; i++ )
   {
       cout << "vals[" << i << "] = ";
       cout << vals[i] << endl;
   }
   return 0;
}

Values before change
vals[0] = 10.1
vals[1] = 12.6
vals[2] = 33.1
vals[3] = 24.1
vals[4] = 50
Values after change
vals[0] = 10.1
vals[1] = 20.23
vals[2] = 33.1
vals[3] = 70.8
vals[4] = 50

int& func() {
   int q;
   //! return q; // Error at compile time
   static int x;
   return x;     // Safe, x remains valid outside the function scope
}