Fundamentals of C and C Programming SubTopics Basic

Fundamentals of C and C++ Programming

Sub-Topics Basic Program Structure Variables - Types and Declarations Basic Program Control Structures Functions and their definitions Input/Output Basic data Structures Miscellaneous EEL 3801 – Lotzi Bölöni

Basic Program Structure The C Preprocessor –Header files –Macros Global data declarations Function prototypes main() function –C/C++ statements Definition of other functions EEL 3801 – Lotzi Bölöni

The preprocessor

The C Preprocessor Obeys special commands called preprocessor directives Indicate certain things to be done to the program code prior to compilation. –Include certain other files when compiling –Replace some code by other code Statements beginning with # are considered preprocessor directives EEL 3801 – Lotzi Bölöni

Header Files The #include directive tells the preprocessor to include the named files in the compilation process. Allows the programmer to: –break up the program across several files for modularity and reusability. –Include Standard C Library files that contain “primitive” functions. EEL 3801 – Lotzi Bölöni

Header Files (cont. ) The #include directive causes a copy of the designated file to be included in place of the directive. Some important ones are: math. h stdio. h stdlib. h string. h EEL 3801 – Lotzi Bölöni

Header Files (cont. ) The format of this directive is: –#include “filename” - the preprocessor searches in the same directory as the file being compiled. Typically for user-defined files. –#include <filename> - the preprocessor searches in pre-defined directories where the standard C Library files are located. Normally used for standard library files. EEL 3801 – Lotzi Bölöni

The #define Directive Symbol replacement Causes the preprocessor to physically replace in the source code prior to compilation, the symbol defined in the macro by the value assigned to that symbol, wherever that symbol is found in the source code. #define PI 3. 14159 EEL 3801 – Lotzi Bölöni

The #define Directive (cont. ) The macro replacement The #define directive can also replace code Macros may be defined either with or without arguments. The replacement code text is put in place of the macro identifier. Arguments should be between parentheses. EEL 3801 – Lotzi Bölöni

The #define Directive (cont. ) Example: #define CIRCLE_AREA(x) ) ( PI * (x) When called: area = CIRCLE_AREA(4); the preprocessor replaces CIRCLE_AREA with ( 3. 14159 * (4) ) EEL 3801 – Lotzi Bölöni

The #define Directive (cont. ) It is important to use parentheses in the definition. Else, confusion to the compiler: area = CIRCLE_AREA(c+2) area = (3. 14159 * (c+2) ) If no parentheses used, however, area = (3. 14159 * c + 2 * c +2) which is incorrect (product takes precedence) EEL 3801 – Lotzi Bölöni

The #define Directive (cont. ) Scope of a macro or symbolic constant is: – until the end of the file –undefined with #undef EEL 3801 – Lotzi Bölöni

Other Preprocessor Directives #if …#endif: can force conditional compilation #error: prints a message displayed as an error message - Page 527 # and ## operators: causes replacement text to be converted to a string - page 527 #line: causes subsequent source code lines to be renumbered from number EEL 3801 – Lotzi Bölöni

Elements of the C language

Global Variable Declarations Global variables should be defined outside of any function. Can include simple variables such as characters, floating point, integers, or complex ones such as arrays, structures and unions. Global type definitions should also be located in this part of the program. EEL 3801 – Lotzi Bölöni

Function Prototypes Tells the compiler: –type of data (if any) returned by function –number of parameters the function expects –the types of each parameter –the order in which the parameters are expected Allows the compiler to validate function calls. Required in C++ but not in C. EEL 3801 – Lotzi Bölöni

Function Prototypes (cont. ) Permits coercion of arguments –Converts one type of data to another required by the function Example: A function called max() will accept 3 integer arguments and return the largest one: int max(int, int); EEL 3801 – Lotzi Bölöni

main() Function The main() function is part of every C and C++ program. Every program in C/C++ begins by executing the main() function No other function is necessary, but main() is. A left brace { defines the beginning of its body, closed by a right brace }. EEL 3801 – Lotzi Bölöni

C Statements Composed of one or more machine level instructions. Conclude with the semicolon ; Could be grouped together as a block of code by using the right and left brackets. { } Example: result = a + b + c * (d + e); EEL 3801 – Lotzi Bölöni

User-Defined Functions C programs typically require several functions besides main(). –Some may be standard C library functions –Others may be user-defined functions This is done to simplify the programming task by splitting various functionality between functions Permits abstraction EEL 3801 – Lotzi Bölöni

Variables

Variables A variable is a memory location identified by a valid identifier. An identifier is a series of digits, letters and underscores (_) but that does not begin with a digit. Can be of any length, but only first 31 characters are recognized by ANSI C. Case sensitive EEL 3801 – Lotzi Bölöni

Variable Attributes Name: the identifier of the memory location Value: the value stored therein Type: the type of value to be stored therein Storage Class Storage duration Scope Linkage EEL 3801 – Lotzi Bölöni

Variable Types The variable can take on a value, which is stored in its memory location. The size of the memory location depends on the type of value being stored. –character –integer –floating point –double precision floating point EEL 3801 – Lotzi Bölöni

Integers Typically 2 bytes long for 16 -bit machines and 4 bytes long for 32 -bit machines. Can be signed or unsigned. Default is signed. Can also be specified as short or long: –short => 2 bytes (16 bits long) –long => 4 bytes (32 bits long) EEL 3801 – Lotzi Bölöni

Integers - Range Bytes Range Signed Range Unsigned 1 -128 to 127 0 to 255 2 -32, 768 to 32, 767 0 to 65, 535 4 -2, 147, 483, 648 to 2, 147, 483, 647 0 to 4, 294, 967, 295 EEL 3801 – Lotzi Bölöni

Characters Actually are integers but with secondary meaning. Typically 1 byte long. Just long enough to fit the ASCII table of character representations. Can be added just like integers, but one must be careful EEL 3801 – Lotzi Bölöni

Floating Point The basic data type for mathematical calculations Designated as single precision Typically 4 bytes long, allowing 7 significant digits and an exponent range of -37 to 38. Example: 3. 25 e-02 = 3. 25 x 10 -2 = 0. 0325 EEL 3801 – Lotzi Bölöni

Double Precision Floating Point Adds more precision and range to the number represented. Employs 8 bytes, allowing for 15 significant digits and a exponent range of -307 to 308 EEL 3801 – Lotzi Bölöni

Extended Precision Floating Pt. Adds even more precision and range. Employs 10 bytes, 19 significant digits and a exponent range of -4931 to 4932 EEL 3801 – Lotzi Bölöni

Variable Type Declarations All variables in C must be declared and typed. This is typically done at the beginning of the program or of a function definition. C++ allows variables to be declared and typed more flexibly, at the location where they are first used. EEL 3801 – Lotzi Bölöni

Variable Type Declarations Integers - basic declaration: int <variable name>; Several variables can be declared in the same statement: int <var 1>, <var 2>, … <varn>; Values can be assigned during declaration: int <var 1> = 25; EEL 3801 – Lotzi Bölöni

Variable Type Declarations Other declarations for integers are: –unsigned int <var>; –unsigned long <var>; –unsigned short <var>; –long int <var>; (int can be omitted) –short int <var>; (int can be omitted) int is signed by default. These are self-explanatory otherwise EEL 3801 – Lotzi Bölöni

Variable Type Declarations Floating point - basic declaration: float <var>; Several variables can be declared in the same statement: float <var 1>, <var 2>, … <varn>; Values can be assigned during declaration: float <var 1> = 25. 0; EEL 3801 – Lotzi Bölöni

Variable Type Declaration Double precision - basic declaration: double <var>; Several variables can be declared in the same statement: double <var 1>, <var 2>, … <varn>; Values can be assigned during declaration: double <var 1> = 25. 0; EEL 3801 – Lotzi Bölöni

Variable Type Declaration The character basic declaration is char <var>; EEL 3801 – Lotzi Bölöni

Variable Type Definition Very different from declaration. Allows the user to define an identifier to describe a new variable type. The new variable type used in lieu of the other in declarations. typedef Example: typedef long unsigned int word; EEL 3801 – Lotzi Bölöni

Determining Variable Size The C unary operator sizeof returns the size of the variable or constant applied to. The “argument” is a data type or constant. Returns the number of bytes required to store a value of a particular type. Parentheses not required, but highly recommended. Example: sizeof(int) returns 2. EEL 3801 – Lotzi Bölöni

Storage Classes Helps determine the variable’s storage duration, scope and linkage. Two basic types: –automatic storage duration auto register –static storage duration extern static EEL 3801 – Lotzi Bölöni

Automatic Storage Class Automatic storage variables are –created when the block in which they are declared is entered. –Exist while the block is active –destroyed when the block is exited Only variables can have automatic storage A function’s local variables are automatic by default. EEL 3801 – Lotzi Bölöni

Automatic Storage Class Thus, auto keyword not used often. Can save memory because memory location is released for re-use when function exits. Example of “principle of least privilege”: Why have something in storage when it is not needed? EEL 3801 – Lotzi Bölöni

External Storage Class External variables are global variables that exist as long as the program exists. Variables declared at the top of the program file are by default external. Variables declared inside blocks can also be declared external through the keyword extern prior to the declaration. Example: extern int temperature; EEL 3801 – Lotzi Bölöni

External Storage Class Linkage The external variable is only good until the end of the file. It can be extended to other files by declaring it again in other files, but the extern keyword in front of it must be used. EEL 3801 – Lotzi Bölöni

Static Storage Class Somewhere between global and automatic. Can be only recognized within the block where it is declared. But outlives the exiting of the function so it can retain its value when the function is called again. EEL 3801 – Lotzi Bölöni

Scope Rules The scope of an identifier is the portion of the program in which the identifier can be referenced. The four scopes are: –function scope –file scope –block scope –function-prototype scope EEL 3801 – Lotzi Bölöni

Scope Rules Only “label identifiers” (colon after them) have function scope. Used to name the location in function. Identifier declared outside of any function has file scope. Known in all functions after it is declared until the end of file. global variables, function definitions function prototypes EEL 3801 – Lotzi Bölöni

Scope Rules Identifiers declared inside a block have block scope. Scope ends after }. –Static local variables have block scope. Storage duration does not affect scope. –Local variables –function parameters variables declared inside function prototype have function-prototype scope. Not recognized outside of prototype. EEL 3801 – Lotzi Bölöni

Sample Program /* Test Program #1 */ #include <stdio. h> void a(void); void b(void); void c(void); int x=1; main() { int x = 5; { int x = 7; } a(); b(); c(); return 0; } /* function prototype */ /* global variable */ /* local to main() */ /* local to block within main()*/ EEL 3801 – Lotzi Bölöni

Sample Program (continued) void a(void) { int x = 25; x = x + 1; . } void b(void) { static int x = 25; x = x + 1. } void c(void) { x = x * 10; } EEL 3801 – Lotzi Bölöni