Presentation 5th

Preprocessor and Underlying C laungage
Chorn Charly
Leang Bunrong
Cheng Udam
Kan Vichhai
Srou Chanthorn
Em Vy
Seth Sambo
Chea Socheat

Content
 #define
 #import
 #include
 #undef
 Conditional compilications
 Array
 Function
 Block
structure
Pointers
Miscellaneous Language Features
How Things Work

Preprocessor
 Preprocessor is the initial program. the first step in compile files it need through initial the
program.(note preprocessor not finish with “ ; ”).
 Preprocessor is begin with #.
 Preprocessor advantages:
1. Define constants(UpperCase All for name convention).
2. Import files to files at specifice point
3. condictionally compile code( use to prevent Program).
4. Reduce coding
Oh ! It is in
.h file.
Preprocessor
Compiler(GCC)
.h file

Preprocessor(cont.)
Source program
Compiled code
Objective – C Compiler(e.g gcc)
Objective – C Preprocessor GCC(objective-C compiler)

Preprocessor(cont.)
 Preprocessor are: #define,#include,#import and conditional compilation ..etc.
1. #define is used to define constants.it also is used to define macro to make easy for develper
that can use own keyword to develop own project( reduce line of codes).
 Syntax: #define constantName value
 Example:

Preprocessor(cont.)
 #import (#include in C language) is the preprocessor to insert the text of the file Header File.h
Into file being processed at the point of the #import line.
 Syntax1: #import “headerName.h”
 Syntax2:#import <package/headerName.h>
 Example:
 Syntax1 is used to import files (class,category...etc) in own project (new class that implement
by new generation).
 Syntax2 is used to import files (package,class...etc) in othe package to our project(build in
classes , libraries ..etc.(Foundation.h,UIKit...etc).

Preprocessor(cont.)
 #if,#ifdef,#ifndef proprocessor is like if statement. but it execute during compile
time(condictionally during compile time).
 Syntax1:
#if identifier(macro or constant)
//statements(macro )
#else
// statements(macro)
#endif
 Example:
 Note: #define is no space . In #if preprocessor between # and define keyword is got a space
character.(#define => # define).

Preprocessor(cont.)
 #ifdef....#endif,#ifndef .......#endif is executed as #if the same.objective – C new version
recomment that should not use #if .it can duplicate include file in compile time.
 Syntax1:
#ifndef identifier(macro or constant)
//statements(macro )
#else
// statements(macro)
#endif
 Note:identifier(macro or constant) we can configure Xcode to create it.
 #if , #ifdef is executed when identifier=1(true) but #ifndef is executed when identifier=0(false).

Preprocessor(cont.)
 To define Constant by configure Xcode.

Preprocessor(cont.)
 To define Constant by configure Xcode. Double click on debug.and add new Constant
Identifier or constant

Preprocessor(cont.)
 #undef is used to reset macro.
 Syntax:
#undef macroname

Array
• Objective-c array represent an entire set of values. Then each value store in the
different element of the set using a number called an index number. Index number start
from 0 to n-1. you can use array anywhere the variable dose. It similar to variable you
need to declare before use. Declare an array involves declaring the type of element that
will be contained in the array.
Int fibonacci [15]; //declare an array named fibonacci with the 15 size
Int integers[5] = {0,1,2,3,4}; // declare an array with initialize
Char letters[5] = {‘a’,’b’,’c’,’d’,’e’}; //declare an array with character
Int a[10] = { [9] = 1 , [2]=3 , [1]=2 , [0]=1}; //declare an array with initialize base the specific type

Array cont….
• The array we used in the last example was a one dimensional array. Arrays can have more than one
dimension, these arrays-of-arrays are called multidimensional arrays. They are very similar to
standard arrays with the exception that they have multiple sets of square brackets after the array
identifier. A two dimensional array can be though of as a grid of rows and columns.
This section will take a look at the two dimension array.
Example in this case it like matrix 4 * 5 show as below
10 5 -3 17 82
9 0 0 8 -7
32 20 1 0 14
0 0 8 7 6
Int M[4][5] = {
{10 , 5 , -3 , 17 ,82 },
{9 , 0 , 0 , 8 , -7} ,
{32 , 20 , 1 , 0 , 14 },
{0 , 0 , 8 , 7 , 6}
};

Block(cont.)
• it can have parameter also
• it can be the parameter of function
• we use it as a parameter, it mean that we want to get the value of the processing of
block in the parameter
• it can not use global variable
• it can only use its own variable in block

Block(cont.)
• Syntax
return-type(^block-name)(parameter-type) = ^(parameter-type and name){
//block-body
}

Block
• default of block or this way

• Accessing
• it is similar to function when we call block to use

Block with parameter
• we can use block with parameter and return type
• accessing

Block with parameter(cont.)
• it can take multiple parameter and more
• accessing

Access outside variable in block
• you can not access outside variable in the block if you try, you will get error like this

Access outside variable in block(cont.)
• solution
• it mean that you declare variable for block can use it

Block as function parameter
• we can use block as a parameter of a function
• file.h

Block as function parameter(cont.)
• file.m
implement body
accessing method

• block as parameter can take two or more parameter in it and return value also
• note parameter-name for block is not importance we do not need to declare the name
but when we call it we need to assign name to it
file.h
we do not need to define a name (optional)

• file.m
we do not need to define a name (optional)

• main method
we need to assign name to it

Structures
• Structure is an entity that contains various types of variable in it

Structures(Cont.)
• Initialize a structure

Structures(cont.)
• Accessing variables in structures

Pointer
• What is pointer?
 A variable that is able to store the address of another variable is called a "pointer”.
 Allows us to indirectly access variables
o In other words, we can talk about its address rather than its value
• Syntax to create pointer:
Datatype *pointer_name.
example: int *a;
 Simple int or float or double variables, they are like a box which can store a single int or float
or double value. Example: int a=10;  a
10
 Let create other variable that using pointer. Example: int *b;  b

Pointer(cont.)
 Can we write int *d = 10 ? NO WE CANNOT. As I told you above pointer variable can only store address
not value. If we write it in Xcode it will show the warning for us.
 And if we still want to print out the *d value we will get this result.
Result:

Pointer(cont.)
 If we write int *d=10, it will look like:
 For now let assign our pointer variable to other value.
Result
D

Pointer(cont.)
• Let’s see how our pointer get value from variable a:
10
a
d 0x103FF
 Variable d is only store address that reference to the variable a.
• Array and pointer;
 I will create an array with 5 elements within it.
 And I will create a pointer that point to it.

Pointer(cont.)
• Let see how it work in memory
• Let print out the value of b:
• So, how can we print out the value of 20?
 It will print out 20.
• What does *(d+1) mean?
 It means that now we are moving the address of d to one block forward.
a[5]
10
20
30
40
50
value
address
x3100
x3101
x3102
x3103
x3104
*b
x3100

Pointer and structure
• We have learned about the structure already. So ,now let make it work with our pointer.

Pointer and structure(cont.)
• So how can we access structure members in our structure?
• Let try to print out all the value:
Or
Or

Pointer and Function
• Let create function with parameters as pointer :

Pointer and Function(cont.)
• How to call and use it :
• Result:

Pointer and Function(cont.)
• So let call swap for the second time:
• The result will be like

The goto Statement
• goto statement cause a direct to specified point in the program.
• To identify where the program to be made you have to create label.
• This label can be located anywhere in the function before or after the goto.
• Syntax:
goto labelName;
labelName: statement;

The Null Statement
• A null statement consist of only a semicolon ( ; ) and perform no operation. When you
place a semicolon ( ; ) wherever a normal program statement appear, known as the null
statement.
• Sometime in the program you place it at the end statement but you can place it after
while, for, do statements to terminate loop expression.
• Example:
null statement

The Comma Operator
• The comma operator ( , ) allows you to use two or expressions where only one
expression is expected. Look at the example:
Output:
• When you evaluate between two operands while assign value to variable a it’ll take the
result and discard the result of variable b.
• One more thing is using in for statement expression.

The sizeof Operator
• Although you never make clear about size of data type in your program, sometimes you
need to know this information.
• Now you can use the sizeof operator to determines sizes.
• Example:

Command-Line Arguments
• Similar to Java when you want to pass some value from the command line to your
Objective-C program when they are executed. These value are called command line
arguments.
• The command line are handle using main() function arguments.

Command-Line Argument (cont.)
• Click  Product  Scheme  Edit Scheme then show this dialog, click add argument.

How Things Works
Because of Objective-C language has the C language underneath so this section
will explain how relationship between Objective C and C language and there are four
factors that we will talk about it.
Fact 1 : Instance Variables Are Store in Structures
In C language to manipulate instance variables or to defines a physically grouped
list of variables to be placed under one name. On the other hand, In Objective C we use
class to manipulate instances and objects.

How Things Works (cont.)
• Fact 2 : An Object Variable Is Really a Pointer
Objective-C has pointers because it is an evolution of C, which used pointers
extensively. In C you may usually use pointer with array or structure and so on. Objective-
C provides convenient access to memory addresses through the use of pointers to
particular types. The main advantage of pointer types is that they allow you to interpret
any memory address as the potential location of a variable.

How Things Works (cont.)
• Fact 3 : Methods Are Functions, and Message Expressions Are Function Calls
Methods are really function. In Objective C, there are sender and receiver that
sender send the message and receiver will receive the message from sender. The way
that we send or receive the message is call sending message that mean calling function.
• Fact 4 : The id Type is Generic Pointer Type
Objective-C provides support for dynamic typing via the id data type. The id type is
a unique Objective-C type that can hold a pointer to any type of Objective-C object,
regardless of its class.

Block
• Block is use like a function but it have some difference from function
• Block can declare out of class it is not follow by class, it can declare everywhere
• Block can not create in file.h, it can create only file.m
• if we create in file.h it is not error at compile time but it is error at runtime
• it follow by Caret sign (^)
• it follow by the semi-colon (;)

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Editor's Notes