C Programming Basics and Execution Flow

Execution and Flow of C Programs

• C programs go through several stages before they can be executed.
• The preprocessor handles preprocessor directives and produces expanded source code.
• The compiler translates the expanded source code into assembly code.
• The assembler converts assembly code into object code, creating an .obj file.
• The linker combines the object code with libraries and produces executable code, creating an .exe file.
• The loader loads the executable code into memory for execution.

First C Program Structure

• The basic C program demonstrates how to print "Hello World".
• It uses the #include directive to include standard input/output functions.
• The main() function is the entry point for program execution.
• The printf() function is used to display output to the console.
• The return 0; statement indicates successful program termination.

C Character Set

• Characters are fundamental building blocks in C programs.
• They form words, numbers, and expressions.
• The C character set includes letters, digits, special characters, and whitespace characters.
• Whitespace characters are ignored by the compiler unless they are part of string constants.

C Character Set Types

• Letters: Includes both uppercase (A-Z) and lowercase (a-z) English letters.
• Digits: Includes decimal digits from 0 to 9.
• Special Characters: Include symbols such as &, #, *, @, %, \, etc.
• Whitespace Characters: Include space, tab, carriage return, newline, form feed, vertical tab.

Tokens

• Tokens are the fundamental units of a C program.
• They are the building blocks used to create a C program.
• Tokens are like individual words within a sentence.
• There are six types of tokens in C: Keywords, Identifiers, Special Symbols, Constants, Strings, and Operators.

Keywords

• Keywords are predefined reserved words in C, each with its own specific meaning.
• They are used by the compiler to define the structure and behavior of a program.
• Cannot be redefined or used as variable names.
• C supports 32 keywords.

Identifiers

• Identifiers are user-defined names given to elements such as variables, functions, and arrays.
• They consist of letters, digits, and underscores.
• The first character must be a letter or underscore.
• Case-sensitive (lowercase and uppercase letters are distinct).
• Identifiers cannot be keywords.

Rules for Identifiers

• Must start with a letter or underscore.
• Can contain letters, digits, and underscores after the first character.
• Cannot contain special characters or spaces.
• Maximum of 31 characters are significant (longer identifiers are truncated).
• Cannot use keywords as identifiers.

Constants

• Constants are values that remain unchanged during program execution.
• They are fixed values assigned to variables.
• Declared using the const keyword.

Constant Types

• Numeric Constants: Represent numerical values.
  • Integer Constants: Whole numbers without decimal points.
  • Real Constants: Numbers with decimal points.
• Character Constants: Represent single characters enclosed in single quotes (e.g., 'A', '5', '$').
• Symbolic Constants: Defined using the #define preprocessor directive (e.g., #define PI 3.14159).

Variables

• Variables are used to store data values that can change during program execution.
• Variables are declared using a data type followed by a variable name.

Variable Assignment

• Simple Assignment: Uses the = operator to assign a single value to a variable (e.g., x = 10;).
• Compound Assignment: Uses expressions to assign values (e.g., y = x + 5;).

Variable Types

• Constant Variables: Declared using the const keyword. Their value cannot be modified after initialization.
• Volatile Variables: Their value can be changed externally by factors outside the program's control.
• Local Variables: Declared within a function or block. They are accessible only within that scope.
• Global Variables: Declared outside any function or block. They are accessible from anywhere in the program.
• Static Variables: Declared using the static keyword. They retain their value between function calls.

Data Types

• Data types define the type of data a variable can store and how much memory it occupies.
• They determine the range of values a variable can hold and the operations that can be performed on it.

Operators

• Operators are special symbols used to perform operations on operands (values).
• They provide the means to manipulate data and control program flow.

Arithmetic Operators

• Used for mathematical operations:
  • + (addition)
  • - (subtraction)
  • * (multiplication)
  • / (division)
  • % (modulo, remainder after division)

Relational Operators

• Compare two values and produce a boolean result (true or false):
  • < (less than)
  • > (greater than)
  • <= (less than or equal to)
  • >= (greater than or equal to)
  • == (equal to)
  • != (not equal to)

This quiz covers the fundamental stages of executing C programs, including preprocessing, compiling, assembling, linking, and loading. It also introduces the structure of a basic C program, specifically focusing on printing 'Hello World' and understanding the C character set. Test your knowledge of these essential programming concepts.