C Functions

Intended Learning Outcomes
• Distinguish the basic concepts of functions
• Differentiate built-in function to user-defined function • Differentiate the functions that do not return a value and functions that return a value.
• Apply or create function/s to solve problems

Function
• known with various names like a method or a sub-routine or a procedure, etc.
• is a group of statements that together perform a task. Every C program has at least one function, which is main(), and all the most trivial programs can define additional functions. Two types of function
• Built-in function
– Functions inside the libraries
– Stdio.h -> printf()
– Math.h -> sqrt()

• User-defined function
– Functions that are declared and defined by programmers. Functions
• You can divide up your code into separate functions. How you divide up your code among different functions is up to you, but logically the division usually is so each function performs a specific task.

Advantages of user defined functions
1. Helps to decompose the large program into small segments which makes programmer easy to understand, maintain and debug.
2. If repeated code occurs in a program. Function can be used to include those codes and execute when needed by calling that function.
3. Programmer working on large project can divide the workload by making different functions

Advantage

Structured Approach

Method-oriented Approach

Dividing code according to its func1onali1es

Functions
• A function declaration tells the compiler about a function's name, return type, and parameters.
• A function definition provides the actual body of the function.

Defining a functions
• The general form of a function definition in C programming language is as follows
Syntax:

Defining a functions
• The general form of a function definition in C programming language is as follows

Parts of Functions
• Return Type:
– A function may return a value.
– The return_type is the data type of the value the function returns. (datatype: int, char)
– Some functions perform the desired operations without returning a value.

Defining a functions
• The general form of a function definition in C programming language is as follows

Parts of Functions
• Function Name
– This is the actual name of the function.
– The function name and the parameter list together constitute the function signature
– Starts with small letters and a verb
– E.x. computeAge(), printName()

Defining a functions
• The general form of a function definition in C programming language is as follows

Parts of Functions
• Parameters
– A parameter is like a placeholder.
– When a function is invoked, you pass a value to the parameter.
– This value is referred to as actual parameter or argument. – The parameter list refers to the type, order, and number of the parameters of a function.
– Parameters are optional; that is, a function may contain no parameters.
– ex. Void computeAge(int byear)

Defining a functions
• The general form of a function definition in C programming language is as follows

Parts of Functions
• Function Body
– The function body contains a collection of statements that define what the function does.

Example: function definition

Example:

same DATA TYPE

Function Declarations
• A function declaration tells the compiler about a function name and how to call the function.
• The actual body of the function can be defined separately • Function declaration is required when you define a function in one source file and you call that function in another file. In such case you should declare the function at the top of the file calling the functions

Function Declarations

Calling a Function
• While creating a C function, you give a definition of what the function has to do. To use a function, you will have to call that function to perform the defined task

Calling a Function
• When a program calls a function, program control is transferred to the called function.
• A called function performs defined task, and when its return statement is executed or when its function-ending closing brace is reached, it returns program control back to the main program.

Calling a Function:Example

Output:
• max() function along with main() function and compiled the source code. While running final executable, it would produce the following result:
Max value is : 200

Example 2
• A program that will compute the age of user by the given birth year.
• Formula?

Age = 2015 – birth Year

Solution1

Take note: if the return type is not void,

it should have a return at the end of your funcAon

Solution2

Take note: if the return type is void, No return is needed

What’s the output?

Passed! 93

Assume num1=4, num2=5

N1 = 5, n2 = 4 Answer: 29

Example 4

Void cannot be placed inside prin6,

nothing to return

Will not compile

Solution

The square root: 25

Function Arguments
• it must declare variables that accept the values of the arguments.
• These variables are called the formal parameters of the function.
• The formal parameters behave like other local variables inside the function and are created upon entry into the function and destroyed upon exit.

Output
• if num1 = 1
– Sum is 7

• If num1 = 2
– Product is 12

• Note: you can place method inside another method. Two ways

• Function call by value
• Function call by reference Function call by value
• The call by value method of passing arguments to a function copies the actual value of an argument into the formal parameter of the function. In this case, changes made to the parameter inside the function have no effect on the argument.

Function call by value
• By default, C programming language uses call by value method to pass arguments. In general, this means that code within a function cannot alter the arguments used to call the function. Consider the function swap() definition as follows.

Function call by value
• Consider the function swap() definition as follows. Function call by value
• Consider the function swap() definition as follows. Result:
Before swap, value of a: 100
Before swap, value of b: 200
After swap, value of a: 100
After swap, value of b: 200

Two ways

• Function call by value
• Function call by reference Function call by reference
• The call by reference method of passing arguments to a function copies the address of an argument into the formal parameter.
Inside the function, the address is used to access the actual argument used in the call.
• This means that changes made to the parameter affect the passed argument.

Function call by reference
• To pass the value by reference, argument pointers are passed to the functions just like any other value. So accordingly you need to declare the function parameters as pointer types as in the following function swap(), which exchanges the values of the two integer variables pointed to by its arguments. Result:

C Variable Declarations
• Local
• Global
• Formal Parameters

Local Declaration
• declared inside a function or block
• They can be used only by statements that are inside that function or block of code.

C Variable Declarations
• Local
• Global
• Formal Parameters

Global Declaration
• defined outside of a function, usually on top of the program.
• hold their value throughout the lifetime of your program and they can be accessed inside any of the functions defined for the program. Global Declaration
• can be accessed by any function.
• is available for use throughout your entire program after its declaration.

Global Declaration
• can be accessed by any function.
• is available for use throughout your entire program after its declaration.

C Variable Declarations
• Local
• Global
• Formal Parameters

Formal Parameters
• are treated as local variables within that function and they will take preference over the global variables.

Formal Parameters

Result:FP

Common Programming Errors
1. It is an error to write a C program without a function named main.
2. It is wrong to define functions with the same name in the same program.

Common Programming Errors
3. There should be no semicolons in a function’s header. Thus, the following is wrong. void something(int x, double y);
{
...
}

Common Programming Errors
4. It is an error to define a function inside another. Therefore, it is wrong to write void something(int x, double y)
{
... void anything(char z)
{
...
}
}

C Function: FAQ
1. What is a function?
In computer programming, functions are also called subprograms. A function consists of a groups or sequence of statements.

C Function: FAQ
2. What types of function are there in C?
There are two types of functions, namely: v pre-defined – those functions that have been written for us (by some other programmers); examples are scanf and printf v user-defined – those functions that we are going to write/implement

C Function: FAQ
3. How do you invoke/call a function that has already been defined?
A function that has been defined by the user is invoked by giving its name and its parameters.

C Function: FAQ
4. Can you call a function inside another function (besides main)?
Yes, any function can be called inside any function. Refrain from invoking a function inside a function with the same name. This will not be a syntactical error, but there are issues that should be resolved first (to be discussed in the next course). In the same way, do not call the function main within any function

C Function: FAQ
5. Can you have a return a value through the function name in a void function?
No. A warning will be generated.
6. Can you have more than one return statement within a function?
Yes. However, only one (1) return statement will be executed only. After executing the return statement, control is returned to the calling function.

Many return statements

C Function: FAQ
7. Can you return more than one value through the function name?
No. A function name is an identifier.
Similar to a variable, a function name can hold only one value at a time

C Function: FAQ
8. Does it matter what name you use in the parameter? No. The parameter need not be the same identifier that we used in the calling function.
What matters is the number of parameters, their respective data types, and their sequence. Final Project
• 5 members in a group
• Transactional based system
– Inventory system
– Reservation system
– POS system
– Ticketing system
(no repetition of system)

• Submit your groupings to your leader
• We will get this on your Lab classes

Assignment #1 finals
• Create a program that will guess the number. • Display higher if the input value is higher than the defined number, otherwise lower
• if the input matches the defined number display “congrats!” ask the user if he/she wants to play again. If yes, go back to guessing game
• Create your own function