Functions, Part 1 of 2Review of Structured ProgrammingFunctionsSlide 4Sample Function CallSample Programmer-Defined FunctionScreenshot of Function ExampleExamining PrintMessage()The Function CallThe Function DefinitionGeneral Function Definition SyntaxUsing Input ParametersSlide 13Good Programming PracticeExample of a Function Header Comment1Functions, Part 1 of 2TopicsUsing Predefined FunctionsProgrammer-Defined FunctionsUsing Input ParametersFunction Header Comments2Review of Structured ProgrammingStructured programming is a problem solving strategy and a programming methodology that includes the following guidelines:The program uses only the sequence, selection, and repetition control structures.The flow of control in the program should be as simple as possible.The construction of a program embodies top-down design.3FunctionsWhen program control encounters a function name, the function is called (invoked).Program control passes to the function.The function is executed.Control is passed back to the place where the function was called.4FunctionsWe have used several predefined functions so far:alert()prompt()document.write()toFixed()parseInt()parseFloat()Programmers can write their own functions.Typically, each module in a program’s design hierarchy chart is implemented as a function.5Sample Function Call alert is the name of a predefined function in the JavaScript language alert(“Hello World!”); this statement is is known as a function call this is a string we are passing as an argument (parameter) to the alert function6Sample Programmer-Defined Function<head><title>Function Example</title><script type="text/javascript"> <!-- function PrintMessage() { alert(“A message for you:\n\nHave a nice day!”); } //--></script></head><body> <script type="text/javascript"> <!-- PrintMessage(); //--> </script></body>7Screenshot of Function Example8Examining PrintMessage()<head><title>Function Example</title><script type="text/javascript"> <!-- function PrintMessage() { alert(“A message for you:\n\nHave a nice day!”); } //--></script></head><body> <script type="text/javascript"> <!-- PrintMessage(); //--> </script></body> Function CallFunctionDefinition9The Function CallPasses program control to the functionMust match the definition in name and number of arguments ........ function PrintMessage() { alert(“A message for you:\n\nHave a nice day!”); } ........<body> <script type="text/javascript"> <!-- PrintMessage(); //--> </script></body>Same name and no arguments (nothing inside of the parentheses)10The Function DefinitionControl is passed to the function by the function call. The statements within the function body will then be executed.function PrintMessage(){ alert(“A message for you:\n\nHave a nice day!”);}After the statements in the function have completed, control is passed back to the place where the function was called.11General Function Definition Syntaxfunction FunctionName ( parameter1, . . . , parametern ){variable declaration(s)statement(s)}If there are no parameters, there should be nothing inside of the ()'s function FunctionName() { ... }There may be no variable declarations.12Using Input ParametersOften it is the case that we would like to be able to share information with the function.It is possible to send input parameters into the function. We can pass information from the place where the function is called. The next slide illustrates sending a single parameter into a function.13<head><title>Function Parameter Example</title><script type="text/javascript"> <!-- function PrintMessage(counter) { var i; for(i = 1; i <= counter; i++) { alert(“Have a nice day!”); } } //--></script></head><body> <script type="text/javascript"> <!-- var counter; counter = prompt("Enter a number:"); PrintMessage(counter); //--> </script></body>14Good Programming PracticeYou should include a function header comment before the definition of each function.This is a good practice and is required by the 104 Coding Standards.Your header comments should be neatly formatted and contain the following information:function namefunction description (what it does)a list of any input parameters and their meaningsa list of any output parameters and their meaningsa description of any special conditions15Example of a Function Header Comment/***************************************************************** PrintMessage - prints a message a specified number of times** Inputs: counter - the number of times the message will be** printed** Outputs: None***************************************************************/function PrintMessage(counter){ var i; for(i = 1; i <= counter; i++) { alert(“Have a nice day!”);
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