COMP 102 Programming Fundamentals I

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COMP 102Programming Fundamentals I

• Presented by Timture Choi

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Parameter Passing

• 4 categories
• Pass-by-value
• Pass-by-result
• Pass-by-value-result
• Pass-by-reference

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Pass-by-value

• Operation
• By using additional storage for the parameters
• The value of parameters are copied to the storage
  allocated
• The storage memory will be destroy after the
  termination of the function
• Characteristics
• If a variable is passed as a parameter
• Its value will not be changed after returning
  from the function
• As the function only manipulates the copy of the
  variable

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Pass-by-value

• E.g.

void Increment(int Number) Number Number
1 cout ltlt "The parameter Number is " ltlt
Number ltlt endl int main() int i 10
Increment(i) cout ltlt "The variable i is "ltlt i
ltltendl return 0
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Pass-by-value

• Advantages
• Increased the reliability of the system
• Because the value of the parameter cannot be
  tampered
• Disadvantages
• If the size of the parameter is very large
• E.g. passing a very large array
• This method would be very inefficient
• Only one output can be produced

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Pass-by-reference

• For inout mode parameters
• Syntax
• lttypegt ltvariablegt
• lttypegt ltvariablegt
• It transmits an access path
• To the called function
• Usually just an address
• Instead of a copy of its value
• If the function changes the parameter value
• The value of corresponding argument will also be
  changed
• Since they share the same memory location

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Pass-by-reference

• E.g.

void Increment(int Number) Number Number
1 cout ltlt "The parameter Number " ltlt
Number ltlt endl int main() int i 10
Increment(i) cout ltlt "The variable i is "ltlt i
ltltendl return 0
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Pass-by-reference

• Advantages
• No extra storage and data copying is needed
• Improve the efficiency
• Value of the actual parameters can be modified
• More flexibly
• Provide multiple output

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Function Summary

• Each function can be designed, coded, and tested
  separately
• Facilitate debugging process
• Both pass-by-value and pass-by-reference can be
  used in the same function

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Scope

• Scope of identifier
• The range of statements in which
• The identifier can be referenced
• E.g.
• Scope of variable area
• Starts just after its declaration
• Ends at the end of the function

double area_of_circle(double radius) double
area area 3.1415 radius radius
return area
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Scope

• Global declaration
• Placed at the beginning of the program file
• Can be accessed/visible anywhere/by any function
  in the program
• Local declaration
• Made inside a block of code
• Cannot be accessed outside the current block
• E.g. only can be access within certain function

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Scope Example

• int y 38
• void fun(int, int)
• int main( )
• int z47
• while(zlt400)
• int a 90
• z a
• z
• y 2 z
• fun(1, 2) return 0
• void fun(int s, int t)
• int r 12
• s r t
• int i 27
• s i

scope of y
scope of fun
scope of z
scope of a
scope of s t
scope of r
scope of i
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Scope

• Note
• Undisciplined use of global identifiers
• May lead to confusion and debugging difficulties
• Better to communicate values between functions
• Through arguments/parameters
• Instead of using global variables

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SUMMARY

• By the end of this lab, you should be able to
• Implement function with both
• Parameter pass-by-value
• Parameter pass-by-reference
• Identify the scope of different identifiers
• Declared global/local variables/constants