Function Overloading and Automatic Type Conversion in C++, Slides of C programming

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Chapter

-Function Overloading

-Function Testing

Overloading

Same function name

Different parameter lists

Two separate function definitions

Function ‘signature’

Function name & parameter list ƒ Must be ‘unique’ for each function definition

Allows same task performed on different data

Overloaded Average() Cont’d

Which function gets called?

Depends on function call itself:

avg = average(5.2, 6.7); ƒ Calls ‘two-parameter average()’ ƒ avg = average(6.5, 8.5, 4.2); ƒ Calls ‘three-parameter average()’

Compiler resolves invocation based on signature of function call

‘Matches’ call with appropriate function ƒ Each considered separate function

Overloading Pitfall

Only overload ‘same-task’ functions

A mpg() function should always perform same task, in all overloads ƒ Otherwise, unpredictable results

C++ function call resolution:

st : looks for exact signature ƒ

nd : looks for ‘compatible’ signature

Overloading Resolution Example

Given following functions:

1. void f(int n, double m);
   2. void f(double n, int m);
      3. void f(int n, int m); ƒ These calls: f(98, 99);

Æ

Calls # f(5.3, 4);

Æ

Calls # f(4.3, 5.2);

Æ

Calls ???

Avoid such confusing overloading

Automatic Type Conversion andOverloading

Numeric formal parameters typically made ‘double’ type

Allows for ‘any’ numeric type

Any ‘subordinate’ data automatically promoted ƒ int Æ double ƒ float Æ double ƒ char Æ double *More on this later!

Avoids overloading for different numeric types

Default Arguments

Allows omitting some arguments

Specified in function declaration/prototype

void showVolume( int length, int width = 1, int height = 1); ƒ Last 2 arguments are defaulted ƒ Possible calls: ƒ showVolume(2, 4, 6); //All arguments supplied ƒ showVolume(3, 5); //height defaulted to 1 ƒ showVolume(7); //width & height defaulted to 1

Default Arguments Example

Display 4.8,page 160

The assert Macro

Assertion: a true or false statement

Used to document and check correctness

Preconditions & Postconditions ƒ Typical assert use: confirm their validity ƒ Syntax: assert(<assert_condition>); ƒ No return value ƒ Evaluates assert_condition ƒ Terminates if false, continues if true

Predefined in library

Macros used similarly as functions

An assert Macro Example

Given Function Declaration: void computeCoin(

int coinValue, int& number, int& amountLeft); //Precondition: 0 < coinValue < 100 0 <= amountLeft < //Postcondition: number set to max. number of coins

Check precondition:

ƒ assert ((0 < currentCoin) && (currentCoin < 100) && (0 <= currentAmountLeft) && (currentAmountLeft < 100)); ƒ If precondition not satisfied Æ condition is false Æ program execution terminates!

assert On/Off

Preprocessor provides means

#define NDEBUG #include

Add ‘#define’ line before #include line

Turns OFF all assertions throughout program

Remove ‘#define’ line (or comment out)

Turns assertions back on

Stubs and Drivers

Separate compilation units

Each function designed, coded, tested separately ƒ Ensures validity of each unit ƒ Divide & Conquer ƒ Transforms one big task Æ smaller, manageable tasks

But how to test independently?

Driver programs

Stubs

Develop incrementally

Write ‘big-picture’ functions first

Low-level functions last ƒ ‘Stub-out’ functions until implementation ƒ Example: double unitPrice(int diameter, double price) { return (9.99); // not valid, but noticeably // a ‘temporary’ value } ƒ Calls to function will still ‘work’

Fundamental Testing Rule

To write ‘correct’ programs

Minimize errors, ‘bugs’

Ensure validity of data

Test every function in a program where every other function has already been fully tested and debugged ƒ Avoids ‘error-cascading’ & conflicting results