Function
- 2. Objective of this session Student able to know definition dan theories of function. Student able to use and create functions. Student able to know theories of variable scope. Student able to identify the scope of variable.
- 3. Function • A function is a block of code that performs a task • A function is a type of procedure or routine. • Some program contains at least one function: main() • Why use functions? ▫ Allow programmer to avoid duplicating code ▫ Allow programs to be broken into manageable tasks • Two categories of function: ▫ Value-returning functions ▫ Void functions
- 4. Value – Returning Function • A value-returning function returns precisely one value after completing its assigned task. ▫ Usually returned to the statement that called function Typically, statement displays return value, uses it in a calculation, or assigns it to a variable ▫ Some value-returning functions E.g., pow(3,2)
- 5. Value – Returning Function • A value-returning function returns precisely one value after completing its assigned task. ▫ Usually returned to the statement that called function Typically, statement displays return value, uses it in a calculation, or assigns it to a variable ▫ Some value-returning functions E.g., pow(3,2)
- 6. Example int
- 7. Void Function void sayHello(string name) { write (“Halloooo “ + name ); } Without Return
- 9. Function Header • Function header: first line in a function definition ▫ Does not end with a semicolon ▫ Begins with returnDataType ▫ Next comes the name of the function Naming rules are the same as for naming variables Name usually begins with a verb ▫ Also has an optional parameterList enclosed in () Lists data type and name of formal parameters Formal parameters store the information passed to the function when it is invoked Formal Parameter
- 10. Function Body • Function body contains instructions the function follows to perform its assigned task ▫ Begins with { and ends with } ▫ The last statement is usually return expression; expression represents the value the function returns to the statement that called it ▫ return statement alerts computer that the function has completed its task Data type of expression must agree with the returnDataType specified in function header
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- 12. Call a function (1) void main(){ int a, b, c; b = 5; c = sum (a, b); write (c); } int sum (int num1, int num2) { int result; result = num1 + num2; return (result); } Calling function Variable, get the return of function
- 13. Call a function (2) void main(){ int a , b, c; a = 9; b = 5; c = sum (a, b); write (c); } int sum (int num1, int num2) { int result; result = num1 + num2; return (result); } Actual Parameter
- 14. Passing Information to a Function • Items passed to a function are actual perameters/ arguments ▫ Can be a variable, named constant, literal constant, or keyword You can pass a variable: by value (a copy of the value is passed), or by reference (the variable address is passed) ▫ Examples calcRectangleArea(2, 3) calcRectangleArea(length, width) pass by value
- 15. Using a Function Prototype • If a function definition appears below main(), you must enter a function prototype above main() ▫ Prototype specifies function’s name, data type of return value and of each formal parameter
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- 17. The Scope and Lifetime of a Variable • A variable’s scope indicates where in the program it can be used ▫ Local or global Local variables are declared within a function or appear in a function’s parameterList Global variables are declared outside of any function and remain in memory until program ends Avoid using global variables in your programs • A variable’s lifetime indicates how long it remains in memory
- 18. Summary A function is a block of code that performs a task. Categories of function: Value-returning functions & Void functions Components of function : Header Function & Body Function Types of Parameter : Formal & Actual Next Recursive Function