if (ID >= 0) {
    return true;            // you're returning from the call here
    bool isValidStatus;     // this statement is never reached
                            // here you are declaring a boolean variable isValidStatus. 
                            // this is not a call to the function of the same name;
}
else{
    cout << "*** Program Terminated ***" << endl;
    exit (0);              // same problem is here. the prog is terminated here
    return false;          // this statement is never reached
}

#include <iostream>
using namespace std;
 
bool isValidStatus( char status ) {
  if (status == 's' || status == 'S' || status == 'c' || status == 'C' || status == 'h' || status == 'H'){
    return true;
  }
  cout << status << " is not valid ! try again" << endl;
  return false;
}
 
char getStatus() {
  char status;
  do {
     cout << endl << "Enter payroll status: ";
     cin >> status;
  } while ( ! isValidStatus(status) ); // repeat until a valid status is entered
  return status;
}
 
int getEmployeeData() {
  int ID = 0;
  cout << "Enter employee ID (0 to exit program ): ";
  cin >> ID;
  if ( ID == 0 ) {
    cout << "bye.." << endl;
    exit (0);     
  }         // terminate program
  cout << "employee ID= " << ID << endl;
  return ID;
}
 
int main() {
   int ID = getEmployeeData();   // read employee ID
   char status = getStatus();    // read Status
   cout << "the status entered was : " << status << endl; 
   return 0;              // main should return an exit-code
}

#include <iostream>
 
using namespace std;
 
bool f()
{
  // Do something and return true or false
}
 
int main()
{
  if ( f() )
    cout<<"f() was true"<<endl;
}

#include <iostream>
 
using namespace std;
 
bool f1()
{
  // Do something and return true or false
}
 
bool f2()
{
  if ( f1() && something else )
    return true;
  else
    return false;
}
 
int main()
{
  if ( f() )
    cout<<"f() was true"<<endl;
}