Function Return Values; Identifier Attributes

Tom Kelliher, CS17

Mar. 20, 1996

Function Return Values

Recall the pow function:

double pow(double x, double y);

double pow(double x, double y)
{
   double value;

   ...

   return value;
}

z = pow(x, 2.0) + pow(y, 3.0);

Some function termination conditions:

• Run-time error (does not return to caller).
• Hits the closing } of the compound block
• Executes a return.
  • return;
  • return <expr>;

Example 1

#include <iostream.h>

// Prototype
int getInput(void);

int main()
{
   int i;
   int j;

   i = getInput();
   j = getInput();

   cout << "i: " << i << endl;
   cout << "j: " << j << endl
   return 0;
}

int getInput(void)
{
   int val;

   cout << "Enter an integer: ";
   cin >> val;

   return val;
}

Sample output:

Enter an integer: 39
Enter an integer: -83
i: 39
j: -83

Example 2

void printInstructions(void)
{
   char c;

   cout << "Would you like instructions (y or n)? ";
   cin >> c;

   if (c != 'y')
      return;

   cout << "HaHa!!! There are no instructions available!!!\n";
   cout << "You don't need instructions anyway.\n";
}

Identifier Attributes

Identifier: variable, symbolic constant, function, etc.

Scope:

The region in which an identifier exists.

• Begins at point of declaration.
• If declared within a block, ends with end of block. Local variable, local scope.
• If declared outside of any block, ends with end of file. Global variable, file scope.

Visibility:

The accessibility of an identifier.

An identifier may be in scope, but not visible:

int i = 1;

f()
{
   cout << i << endl;
}

g()
{
   double i = 2.0;

   cout << i << endl;

   {
      int i = 3;

      cout << i << endl;
   }

   cout << i << endl;
}

Program Fragment Example

// beginning of file
int a;

void f(void)
{
   int b;
   ...
}

int c;

void main()
{
   int d;

   {  int a;
      ...
      a;

      ::a;
   }

   int b;
   ...
}
// end of file

Global scope resolution operator: ::.

Variable, symbolic constant lifetime:

The time, during program execution, that memory (RAM) is allocated for the variable or constant.

• Static --- Corresponding to global identifiers.
• Local --- Corresponding to local identifiers.
• Dynamic --- We haven't seen this yet.

Program Design Problem

Design a program which computes factorials. The program should accept positive integers from the user, asking them if they want to continue, and output the factorial of the input.