Advanced Computer Programming

Transcription

1 Hazırlayan Yard. Doç. Dr. Mehmet Fidan

2 Functions are integrities of variables and expressions that are used to fulfill a job. They take definite parameter types and have definite return types. They can be called again and again from other code sections of a program. Basic definition: return_type Funtion_name (Parameters)

3 A function allows you to encapsulate a piece of code and call it from other parts of your code. You may very soon run into a situation where you need to repeat a piece of code, from multiple places, and this is where functions come in. <visibility> <return type> <name> ( <parameters> ) { } <function code>

4 To call a function, you simply write its name, an open parenthesis, then parameters, if any, and then a closing parenthesis, like this: DoStuff(); public void DoStuff () { Console.WriteLine("I'm doing something..."); } The first part, public, is the visibility, and is optional. If you don't define any, then the function will be private. More about that later on. Next is the type to return. It could be any valid type in C#, or as we have done it here, void. A void means that this function returns absolutely nothing. Also, this function takes no parameters, as you can see from the empty set of parentheses, so it's actually just a tad bit boring. Let's change that:

5 Function is composed of function definition, and statements surrounded by curly brackets: private float add( int a, int b, int c) { float t; } t = a + b + c ; return t; Note: Curly brackets determines stating and ending point of a function.

6 private float add( int a, int b, int c) { float t; t = a + b + c ; return t; } Variables a, b and c are valid only in function add. Variable t which is defined in the function add is valid only in the function and deleted after function execution is finished.

7 Functions use keyword return to return a result to calling. If return type is void, then we don t need to use keyword return. return keyword should return a value with a type that should exactly match with the type defined in the function. private float add( int a, int b, int c) { float t; } t = a + b + c ; return t;

8 Function definition should be taken into account while calling a function. Function parameters could be constants as well as variables. Usually the value returned from function is assigned to a variable. value = add( i, j, k ); or value = add( 5, x, 2.7 );

9 When add function is called from main() function, the values that resides in main() data section are copied to the data section of add() function. main() data section i 12 j 25 copied copied add() data section a b 45 k copied c 45

10 EXERCISES Ex-1: Adding Two Integers Ex-2: Write a function which calculates the factorial of a given number. This function will return 0 from numbers smaller than zero and returns 1 for numbers 0 and 1. Calculate the factorial of numbers by using a loop for numbers greater than 1. Write a main function that prints the factorials of numbers between 1 and 10.

11 EXERCISES Ex-3: Write a function that takes two parameters and returns the differences of factorials of these two numbers. Function prototype: int factorial_difference(int a, int b) This function may call the factorial() function written before.

12 VALUE and REFERENCE Functions accepts two types of parameters. value Reference By Value: Instead of actual parameters, copies of parameter values are used while calling a function. By Reference: Addresses of parameters are send while calling a function. If function modified the variable at this address, then the actual value is modified (e.g. The main variable in main function)

13 Value main() data section i 12 Copy of swap() data section parameter 12 a Reference main() data seciton &i 12 Actual swap() data section &i parameter 12

14 ref keyword is used for sending the actual parameter itself to a funtion as a parameter. In the function definition, you should put ref keyword in front of the parameter which meant to be used as reference parameter. Similarly, ref keyword is used before reference variable while function is called.