Value Returning Functions

1
Value Returning Functions

• // Function prototype
• int Largest(int num1, int num2, int num3)
• Function Name
• Type
• Parameters
• Type of parameters
• Formal parameters
• Actual parameters
• float sqrt(float x)
• char myFunction(float param1, int param2,
• char param3)
• -----

2
Function Calls

• // Function prototype
• int Largest(int num1, int num2, int num3)
• float sqrt(float x)
• char myFunction(float param1, int param2,
• char param3)
• // Function calls
• max Largest(score1, score2, score3)
• // Must follow the prototype!
• // Do not include types!
• cout
• sqrt(delta)
• // Error
• // Must use the return value
• chaVal myFunction(50.5, 143, M)

3
VOID Functions

• void DisplayResult(float avg, float max, float
  min)
• // Function type void (does not return any
  value)
• // Decompose a program into smaller functions
• // Programming Rule each function can have at
  most 30 lines!
• int main()
• float score, avg, highest, lowest
• int numScores, loopCount 0
• // input scores
• // Compute avg, highest and lowest
• // output results
• DisplayResult(avg, highest, lowest)
• return 0

4
VOID Functions

• void DisplayResult(float avg, float max, float
  min)
• // Programming Rules Each function must have a
  description!
• // The function displays avg, max and min in
  required format.
• void DisplayResult(float avg, float max, float
  min)
• cout
• cout
• avg
• max
• min
• // return control, no value
• return
• -----

5

• Functions without Parameters
• void UserInstruction()
• int main()
• float score, avg, highest, lowest
• int numScores, loopCount 0
• UserInstruction()
• // input
• // process
• DisplayResult(avg, highest, lowest)
• return 0

6

• // Programming Rules Each function must have a
  description!
• // The function displays user instructions.
• void UserInstruction()
• cout
• section "
• number of "
• range of "
• return

7
Example

• void DisplayMenu()
• int main()
• DisplayMenu()
• void DisplayMenu()
• cout
• return

8
Scope of Variables

• The region of code where it is legal to
  reference (use) an identifier.
• Local Scope
• Global Scope
• -----

9
Code Block

• Between a matching pair of braces
• The body of a function
• int main()
• int alpha 10
• // A block for if statement
• if (alpha 3)
• int n
• cin n
• alpha 3
• return 0
• -----

10
Local Scope
int main() int alpha 10 // A code
block if (alpha 3) int n
cin n alpha n cout n

The scope of an identifier declared inside a
block extends from the point of declaration to
the end of that block.

11
Global Scope

• The scope of an identifier declared outside all
  functions (and classes) extends from the point of
  declaration to the end of the entire source file.
  
• Programming Rules
• No global variables!

12
Class Scope

• CS243

13
Scope of Function Parameters

• Formal parameters
• Local scope
• Same as local variable
• Cannot reference it outside the function
• Receive values on function call
• Actual parameters (no global variables)
• Local scope
• Cannot reference it inside the called
  function

14
Example
// Precondition op is C or S //
Postcondition the cube of // num is computed
when op is // C, and the square of num // is
computed when op is S. int DoIt(int num, char
op) if (op C) result pow(num,
3) else result pow(num, 2)
return result // Assume is
included // What is wrong?

• int DoIt(int num, char op)
• int main()
• int base, result
• char choice
• cout
• cin base
• cout
• cin choice
• while (choice ! C choice ! S)
• cout
• cin choice
• result DoIt(base, choice)

15
Precondition and Postcondition
// Precondition op is C or S //
Postcondition the cube of // num is computed
when op is // C, and the square of num // is
computed when op is S. int DoIt(int num, char
op) int result if (op C)
result pow(num, 3) else result
pow(num, 2) return result

• int DoIt(int num, char op)
• int main()
• int base, result
• char choice
• cout
• cin base
• cout
• cin choice
• while (choice ! C choice ! S)
• cout
• cin choice
• result DoIt(base, choice)

16
Parameter Names

• Meaningful names
• Formal and actual parameters can have the same
  name
• They are different variables in different scopes
• Normally they have different names

17
Trace in HiC

• Largest.cpp
• Local Variables
• Parameters
• Same name
• -------

18
Lifetime of a Variable

• Lifetime
• The period of time during program execution
  when an identifier has memory allocated to it.
• Automatic variables
• A variable for which memory is allocated and
  deallocated when control enters and exits the
  block it is declared.
• Static variables
• A variable for which memory remains allocated
  throughout the execution of the entire program.

19
Program 2

• Due Date Monday, Feb 26
• Grace Date Thursday, Mar 1
• Individual Assignment
• OK to get LIMITED help from others
• DO NOT work as a group
• DO NOT copy from others
• DO NOT let others copy your code
• Program Plagiarism