Function Calling Functions

1. A function can call another function.
   
   
2. Not too surprising since the main function can call any other function.
   
   
3. In CS1124, we'll see that a function can even call itself.
   
   
4. The only restriction is that the prototype must appear before the function is used.
   
   
5. //Program to illustrate a function calling another function.
   //The user enters 2 integers from the keyboard.
   //The program displays the numbers in increasing order.
   
   #include<iostream>
   using namespace std;
   
   void getInput(int& input1, int& input2);
   //Reads two integers from the keyboard.
   
   void swapValues(int& variable1, int& variable2);
   //Interchanges the values of variable1 and variable2.
   
   void orderNumbers(int& n1, int& n2);
   //Orders the numbers in the variables n1 and n2
   //so that n1 <= n2.
   
   void displayResults(int output1, int output2);
   //Outputs the values in output1 and output2.
   //Assumes that output1 <= output2
   
   
   int main( )
   {
         int firstNum, secondNum;
   
         getInput(firstNum, secondNum);
         orderNumbers(firstNum, secondNum);
         displayResults(firstNum, secondNum);
   }
   
   
   //Uses iostream:
   void getInput(int& input1, int& input2)
   {
         cout << "Enter two integers: ";
         cin >> input1 >> input2;
   }
   
   void swapValues(int& variable1, int& variable2)
   {
         int temp;
   
         temp = variable1;
         variable1 = variable2;
         variable2 = temp;
   }
   
   void orderNumbers(int& n1, int& n2)
   {
         if (n1 > n2)
         swapValues(n1, n2);
   }
   
   //Uses iostream:
   void displayResults(int output1, int output2)
   {
         cout << "In increasing order the numbers are: "
               << output1 << " " << output2 << endl;
   }