Called a Function Prototype Function Prototypes (continued) Definition:– a Function Prototype in C is a language construct of the form:– return-type function-name (parameter declarations); I.e., exactly like a function definition, except with a ';' instead of a body in curly brackets Purposes of Function Prototype So compiler knows how to. A function is a block of code which only runs when it is called. You can pass data, known as parameters, into a function. Functions are used to perform certain actions, and they are important for reusing code: Define the code once, and use it many times. & Functions are easier to write and understand & The arguments are seperated by commas & The body of the function may consist of one or many statements & It cannot be defined within another function & Function prototype is a function declaration that specifies the data types of the arguments & Calling one function from within another is said to. View Function In C PPTs online, safely and virus-free! Many are downloadable. Learn new and interesting things. Get ideas for your own presentations. Share yours for free! World's Best PowerPoint Templates - CrystalGraphics offers more PowerPoint templates than anyone else in the world, with over 4 million to choose from. Winner of the Standing Ovation Award for “Best PowerPoint Templates” from Presentations Magazine. They'll give your presentations a professional, memorable appearance - the kind of sophisticated look that today's audiences expect.
Functions 'Encapsulate' a task (they combine many instructions into a single line of code). Most programming languages provide many built in functions that would otherwise require many steps to accomplish, for example computing the square root of a number. In general, we don't care how a function does what it does, only that it 'does it'!
When a function is 'called' the program 'leaves' the current section of code and begins to execute the first line inside the function. Thus the function 'flow of control' is:
- The program comes to a line of code containing a 'function call'.
- The program enters the function (starts at the first line in the function code).
- All instructions inside of the function are executed from top to bottom.
- The program leaves the function and goes back to where it started from.
- Any data computed and RETURNED by the function is used in place of the function in the original line of code.
Why do we Write Functions?
They allow us to conceive of our program as a bunch of sub-steps. (Each sub-step can be its own function. When any program seems too hard, just break the overall program into sub-steps!)
They allow us to reuse code instead of rewriting it.
Functions allow us to keep our variable namespace clean (local variables only 'live' as long as the function does). In other words, function_1 can use a variable called i, and function_2 can also use a variable called i and there is no confusion. Each variable i only exists when the computer is executing the given function.
Functions allow us to test small parts of our program in isolation from the rest. This is especially true in interpreted langaues, such as Matlab, but can be useful in C, Java, ActionScript, etc.
Steps to Writing a Function
- Understand the purpose of the function.
- Define the data that comes into the function from the caller (in the form of parameters)!
- Define what data variables are needed inside the function to accomplish its goal.
- Decide on the set of steps that the program will use to accomplish this goal. (The Algorithm)
Parts of a 'black box' (i.e., a function)
Functions can be called 'black boxes' because we don't need to know how they work. Just what is supposed to go into them, and what is supposed to come out of them.
When defining a program as a black box, we must describe the following attributes of the function.
Note: most documentation systems are just this, the attributes of a function with no code associated with it.
The Name - describes the purpose of the function. Usually a verb or phrase, such as 'compute_Average', or just 'average'.
The Inputs - called parameters. Describe what data is necessary for the function to work and gives each piece of data a Symbolic Name for use in the function.
The Calculation - varies for each function
The Output - Usually one (but sometimes zero or sometimes many) values that are calculated inside the function and 'returned' via the output variables.
Function Workspace
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Every function has its own Workspace. This means that every variable inside the function is only usable during the execution of the function (and then the variables go away).
Having a separate 'workspace' for each function is critical to proper software engineering. If every function shared every variable in an entire program, it would be easy to inadvertently change the values of variables that you shouldn't. Further, it would be hard to remember what 'names' have been used elsewhere, and coming up with new names to represent similar ideas would be challenging.
A side-effect of function variables not existing after the end of the function is that the only way to get information 'out' of a function is by 'returning' that information via the output of the function.
Additionally, the function can only 'see' the information that is 'passed' to it via parameters. Thus the only way information can get 'in' to the function is by using parameters.
Note: In certain object oriented languages (e.g., C++, Java, ActionScript), a function can also see all of the variables associated with its containing object.
Formal vs. Actual Parameters
When we create a function, it should represent a 'generic' action that can be applied in many circumstances. For example, if we want to find the average grade, it doesn't matter if it is on a test, or on a quiz, or an assignment, or a midterm, etc... given any list of grades we can compute an average!
...but if it can be any list of grades, how do we know what the list of grades will be called? The answer: we don't care. You, the programmer of the function, provide your own name for the data. This is much the same as when a sales person calls you and reads a script trying to sell something to you, they say: Dear _insert customer name here_, let me sell you our wonderful product.
When writing a function, the programmer must provide a blank to plug in what ever data is of current interest; the blank should have a good symbolic name saying what it will represent. Here is a pseudocode function example:
Inside the average_grade function, the name list_of_grades will be used in place of whatever variable some other user has stored his or her grades in. Thus to call the function, I might write:
In 'My' code, the grades are stored in the variable, 'midterm_grades'. Inside the function, the grades are stored in the variable 'list_of_grades'. Thus, during the execution of the program, both names will refer to the same thing but at different times.
The parameter 'list_of_grades' is called a Formal paramater; again, this just means a place holder name for any possible set of grades.
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The variable midterm_grades is the Actual paramater. This means 'what is actually used' for this call to the function, such as [90, 100, 70];
Nesting Functions?
Often the question comes up: Can we Nest functions (can we place the code for one function inside another function)? The answer is a resounding: NO!
It should be noted, that we can utilize (call) other functions inside a function, but we cannot create the recipe for a new function there.
Note: Sadly this question often comes up when we are careless with our indentation and syntax, and accidentally forget to end our first function, thus, to the computer, placing our second function inside our first function:
Back to Topics List A function depending an whether the arguments are present or not and whether a value is returned or not, may belong to one of following categories
- Function with no return values, no arguments
- Functions with arguments, no return values
- Functions with arguments and return values
- Functions with no arguments and return values.
1.).In this category, the function has no arguments. It does not receive any data from the calling function. Similarly, it doesn’t return any value. The calling function doesn’t receive any data from the called function. So, there is no communication between calling and called functions.
2.)In this category, function has some arguments . it receives data from the calling function, but it doesn’t return a value to the calling function. The calling function doesn’t receive any data from the called function. So, it is one way data communication between called and calling functions.
Eg: Printing n Natural numbers
Output:
Enter n value: 5
1 2 3 4 5
Note:
In the main() function, n value is passed to the nat() function. The n value is now stored in the formal argument n, declared in the function definition and subsequently, the natural numbers upto n are obtained.
3.)In this category, functions has some arguments and it receives data from the calling function. Simillarly, it returns a value to the calling function. The calling function receives data from the called function. So, it is two-way data communication between calling and called functions.
Eg:
Output:
Enter n: 5
Factorial of the number : 120
4.)In this category, the functions has no arguments and it doesn’t receive any data from the calling function, but it returns a value to the calling function. The calling function receives data from the called function. So, it is one way data communication between calling and called functions.
Eg:
Many a times, we need to repeat the same process in a program multiple times. It is difficult for us to define functions for every function call of the same process.Based on the calling of the functions by the user in a program, functions are classified as
- Recursive functions
- Non-Recursive functions
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