Unit 1: Basics and introduction to C

1. The C Character Set

The C character set consists of the alphabet, digits, and special characters used to represent information. These characters are combined to form strings, variables, and constants.

• Alphabets: Uppercase (A to Z) and Lowercase (a to z). C is case-sensitive, meaning A and a are different.
• Digits: Decimal digits 0 through 9.
• Special Characters: Symbols with specific meanings, such as:
  • ,, ., ;, :, ?, ', "
  • |, /, \, ~, _
  • $, #, %, &, ^, *
  • -, +, <, >, =, (, ), {, }, [, ]
• White Space Characters: Used to separate words but are generally ignored by the compiler during execution. Includes blank space, newline (\n), horizontal tab (\t), vertical tab (\v), and carriage return (\r).

2. Identifiers and Keywords

Keywords

Keywords are reserved words in C that have a predefined meaning to the compiler. They cannot be changed or used as variable names. There are 32 standard keywords in ANSI C:

Identifiers

Identifiers are user-defined names given to program elements like variables, functions, and arrays.

Rules for Naming Identifiers:

1. Must begin with a letter (A-Z or a-z) or an underscore (_).
2. Followed by any combination of letters, underscores, or digits (0-9).
3. No special characters (like @, #, %) allowed other than underscore.
4. No white spaces allowed.
5. Keywords cannot be used as identifiers.
6. Case-sensitive (Total and total are different).

3. Data Types

Data types specify the type of data a variable can hold, the storage space required, and the range of values it can represent.

Primary Data Types

• char (Character):
  • Size: 1 byte.
  • Range: -128 to 127 (signed) or 0 to 255 (unsigned).
  • Format specifier: %c.
• int (Integer):
  • Size: Usually 2 or 4 bytes (machine-dependent).
  • Stores whole numbers.
  • Format specifier: %d.
• float (Floating Point):
  • Size: 4 bytes.
  • Stores decimal numbers (6 decimal places precision).
  • Format specifier: %f.
• double (Double Precision):
  • Size: 8 bytes.
  • Stores decimal numbers with higher precision (15 decimal places).
  • Format specifier: %lf.
• void:
  • Represents the absence of value. Used in functions that do not return a value.

4. Constants and Variables

Variables

A variable is a named storage location in memory used to hold a value that can change during program execution.

Declaration vs. Initialization:

int age;          // Declaration (reserves space)
age = 25;         // Assignment
int score = 100;  // Initialization (Declaration + Assignment)

Constants

Constants are fixed values that do not change during the execution.

1. Integer Constants: Whole numbers (e.g., 10, -5, 07 (Octal), 0xF (Hex)).
2. Real (Floating-point) Constants: Numbers with fractions (e.g., 3.14, -0.005).
3. Character Constants: Single character in single quotes (e.g., 'a', '5').
4. String Constants: Sequence of characters in double quotes (e.g., "Hello").
5. Symbolic Constants: Defined using #define or const.
   • #define PI 3.14 (Preprocessor directive)
   • const int MAX = 100; (Keyword)

5. Expressions

An expression is a combination of variables, constants, and operators that evaluates to a single value.

• Example: result = (a + b) * c;

Operator Precedence and Associativity:
Determines the order in which operations are performed. For example, multiplication * has higher precedence than addition +.

6. Operators in C

Operators are symbols used to perform operations on operands (variables/values).

A. Arithmetic Operators

Used for mathematical calculations.

B. Unary Operators

Operate on a single operand.

• Increment (++): Increases value by 1.
  • Pre-increment (++a): Increment first, then use value.
  • Post-increment (a++): Use value first, then increment.
• Decrement (--): Decreases value by 1.
• Unary Minus (-): Negates the value.
• Sizeof (sizeof): Returns the size of a variable/type in bytes.

C. Relational Operators

Used to compare two values. Returns 1 (true) or 0 (false).

D. Logical Operators

Used to combine conditional statements.

Note: C uses Short-circuit evaluation. In (A && B), if A is false, B is not evaluated.

E. Assignment and Conditional Operators

Assignment Operators:

• Simple: = (Assigns right side to left side).
• Compound (Shorthand): +=, -=, *=, /=, %=.
  • a += b is equivalent to a = a + b.

Conditional (Ternary) Operator (? :):
It is a shorthand for if-else.

• Syntax: Condition ? Expression1 : Expression2;
• Logic: If Condition is true, execute Expression1; otherwise, execute Expression2.
• Example: max = (a > b) ? a : b;

F. Bitwise Operators

These operators perform operations at the bit level (binary representation).