OSU CSE 2421
Required Reading:
Computer Systems: A Programmers Perspective, 3rd Edition,
Chapter 1 thru Section 1.3
Pointers on C,
Chapter 5 thru Section 5.1.3, 5.3 through the end of the chapter
J.E.Jones
OSU CSE 2421
Libraries
(e.g., printf() code)
Assembler
hello.c
Type in program source code (file.c) using an editor of your choice; plain text
% gcc o hello hello.c
Source code
.c + .h = .i which is the ultimate source code i.e., #includes expanded and #defines replaced, comments removed
Preprocessor
hello.i
C syntax parser
.i .s which is assembler source code
Compiler
Assembly Code (hello.s)
Assembler code parser
.s .o which is an object file; fragments of machine code with unresolved symbols, i.e., some addresses not yet known (vars/subrs).
Object Code (hello.o)
Link Editor/ Linker
.o + library links a.out (default name); resolves symbols, generates an executable
Executable Code
hello
% hello [executes the program]
J.E.Jones
OSU CSE 2421
Basic Data Types
Constants
Variables
Identifiers
Keywords
Operator Precedence and Associativity
Basic I/O (covered in a separate set of slides)
Control structures (if, while, for, etc.)
(covered in a separate set of slides)
Can you associate one of the 4 programming language categories to each of these???
J.E.Jones
OSU CSE 2421
Note that variables of type char are guaranteed to always be one byte. All others can differ depending upon the processor being used.
Integer Types
char smallest addressable unit, *always* 8 bits (1 byte); each byte has its own
Floating Point Types (these are usually inexact, well see why later)
float single precision (about 6 decimal digits of precision), (4 bytes)
double double precision (about 15 decimal digits of precision) (8 bytes)
long double about 30 decimal digits of precision (only C99 and after) (16 bytes) double is constant default value; for 4 bytes values use f suffix
address. This data type IS NOT just ASCII characters.
short not used as much; typically, is 16 bits (2 bytes)
int default type for an integer constant value; typically, is 32 bits (4 bytes)
long do you really need it?; typically, is 64 bits (8 bytes)
long long at least 64 bits, sometimes 128 bits, (only supported in C99 and after)
There is no fixed or maximum size for a type in C (except for char; otherwise, size depends on implementation), but the following relationships must hold:
sizeof(char) <= sizeof(short) <= sizeof(int) <= sizeof(long)<=sizeof(long long) sizeof(float) <= sizeof(double) <= sizeof(long double) True size of data types is dependent upon the size of the processor being used.J.E.JonesOSU CSE 2421 Beside the basic types, there is a conceptually infiniteclass of derived types constructed from thefundamental types in the following ways: arrays of objects (variables or derived types) of a given type; pointers to objects of a given type; structures containing a sequence of objects (variables or derived types) ofvarious types; unions capable of containing any of one of several objects of varioustypes. In general, these methods of constructing data types(variables or derived types) can be applied recursively An array of pointers to some type An array of characters (i.e., a string) Structures that contain pointers And so on.J.E.JonesOSU CSE 2421charA, b, 0x42 (hexadecimal), 127, -7unsigned char, 255u, 127123, -1, 2147483647, 040 (octal), 0xab (hexadecimal) 123u, 2107433648, 040U (octal), 0xc2 (hexadecimal) 123L, 0x1FFFl (hexadecimal)123ul, 0777UL (octal)1.23F, 3.14e+0f1.23, 2.7182818281.23L, 9.99E-9Lintunsigned int long unsigned long floatdoublelong double Special characters Not convenient to type on a keyboardUse single quotes (e.g.,
)Looks like two characters but is really only onea b f
r t valert (bell) character backspaceformfeednewline\ backslash? question markcarriage return horizontal tab vertical tab single quote” double quoteooo octal numberxhh hexadecimal numberJ.E.JonesOSU CSE 2421 2 ways (both legal) Put the const keyword after the type keyword, or before the type keyword Note: The compiler treats these as variables to which any assignment is invalid. This means the declared const must be initialized with its (constant) value as part ofthe declaration, because the compiler will not allow statements which makeassignments to it later! Treated as a read-only variable. For program readability, pick one of the two ways and use it exclusively. Beconsistent! Examples:float const PI = 3.141593f; (f is used after value because double is default) const float PI = 3.141593f; Convention is to use uppercase for declared constants, also for those with #define (see below). Symbolic constants (with the #define directive – below) can be used anywhere a literal constant can be used, but constants defined with the const keyword can only be used where variables can be used. More on this later (with examples). We will say more about constants as function parameters, pointers to constants, and constant pointers later.J.E.JonesOSU CSE 2421 A name that substitutes for a value that cannot be changed Can be used to define: Constant Statement Mathematical expression Uses a preprocessor directive: #define
REMINDER: No semi-colon is used for preprocessor directives. Coding convention is to use all capital letters for the name:
#define AREA(r) (3.141593 * r * r)
#define AREA (PI*r*r)
What might happen if parentheses arent included in these define statements?
What if these statements used addition/subtraction rather than multiplication?
Can be used any place you would use the actual value
All occurrences are replaced by the preprocessor before the program is compiled by the compiler.
Examples:
The use of EXIT_SUCCESS in hello.c code
#define PI 3.141593
#define TRUE 1
J.E.Jones
OSU CSE 2421
Purpose: define a variable (can also be a constant) before it is used.
Format: type identifier (, identifier) ; Note: the parentheses here indicate any
number of identifiers, each preceded by a comma
Initial value: can be assigned, but is not required (unless it is a constant)
inti,j=5,k;
char code, category;
inti=123;
const float PI = 3.1415926535f;
double const PI = 3.1415926535;
Type conversion: aka, type casting
Directing the compiler to use a variable as a different type than the one
used in the declaration.
Casting larger types to smaller types is dangerous (truncation
occurs) and should be done with extreme caution!!!
To cast a variable to a different type explicitly, use: (type) identifier
inti=65;
char ch; /* range -128 to 127 */
ch=(char)i; /*Whatisthevalueofch?*/
What happens if we change the initial value of i to 165?
J.E.Jones
OSU CSE 2421
Identifier Naming Rules: names for variables, constants, types and functions. Can use a-z, A-Z, 0-9, and _ (i.e., alphanumeric, digits, and underscore) No other characters can be used
Case sensitive
The first character must be a letter or _ (Usually dont use _ , though, because it is used for operating system purposes).
Keywords are reserved words, and may not be used as identifiers (See the following slide for C keywords)
No guarantee that any value past the 31st character will be recognized. (i.e., will let you use more characters, but no guarantee that it will parse it.)
Identifier Naming Style (the grader will enforce these)
Separate words with _ (this is the original style in C) OR capitalize the first
character of each word after the first (e.g., char_count or charCount) Use all UPPERCASE for symbolic constants or macro (code chunk)
definitions.
Be consistent. Be consistent. Be consistent.
Be meaningful: Write self-documenting code; i.e., identifiers should give a
clear idea of what a variable, constant, type or function is being used for. Sample Identifiers
i0, j1, student_name, studentName, student_score, studentScore
J.E.Jones
OSU CSE 2421
char US_Social_Security_Identification_LastName[50]; char US_Social_Security_Identification_FirstName[50];
Declares 2 50-character arrays
Symbol table for identifier names might only be 32 long (strings must be NULL terminated in C)
12345678911111111112222222222333 01234567890123456789012
US_Social_Security_Identificati 0
J.E.Jones
OSU CSE 2421
Purpose: reserves a word or identifier to have a particular meaning
The meanings of keywords and, indeed, the meaning of the notion of
keyword differs widely from language to language.
You shouldnt use them for any other purpose in a C program. They are
allowed, of course, within double quotation marks (as part of a string to be assigned or printed, for example; this is not using an identifier, actually).
This chart will be supplied to you as a reference for the midterm exam
J.E.Jones
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