Unit 1: Introduction to C Language and Basic Statements

Introduction to C Language

The C language is a powerful, general-purpose, procedural programming language developed in the 1970s by Dennis Ritchie at Bell Labs. It is called a "middle-level" language because it combines the features of high-level languages (like Python or Java) with the low-level control of assembly language.

Key Features:

• Structured: Code can be broken down into blocks and functions.
• Compiled: C code is translated into machine code by a compiler, making it very fast.
• Portable: Code written on one machine can be compiled and run on another with minimal changes.
• Case-Sensitive: main and Main are treated as two different names.

C Characters

The C character set is the set of valid characters that can be used to write C programs.

• Alphabets: A-Z, a-z
• Digits: 0-9
• Special Characters: `+ - * / % = ( ) { } [ ] < > . , ; : ' " # ! & | ~ ^ _ \ ? $`
• Whitespace: Blank space, newline, tab, etc.

Constants and Variables

Variables: A variable is a named location in memory used to store data. In C, every variable must be declared with a specific data type before it can be used.

Constants: Constants are fixed values that do not change during program execution.

There are two main types of constants:

• Literal Constants: The value itself, e.g., 5, 3.14, 'A', "Hello".
• Symbolic Constants: A name given to a literal constant.
  • Using `const` keyword: const float PI = 3.14159;
  • Using `#define` preprocessor: #define PI 3.14159

Declaration Statement

A declaration statement introduces a variable to the compiler. It specifies the variable's data type and its name.

Syntax: data_type variable_name;

Common Data Types:

You can declare multiple variables: int a, b, c;

You can also initialize at declaration: int count = 0;

Arithmetic Expression and Statement

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

A **statement** is a complete instruction to the computer, usually ending in a semicolon (`;`).

Arithmetic Operators:

• + (Addition)
• - (Subtraction)
• * (Multiplication)
• / (Division) - Note: Integer division truncates the decimal (e.g., 5 / 2 is 2).
• % (Modulus) - Gives the remainder of a division (e.g., 5 % 2 is 1).

Example Expression: (a + b) * 10
Example Statement: area = 0.5 * base * height;

Assignment Statement

The assignment statement uses the assignment operator (=) to store the value of an expression into a variable.

Syntax: variable_name = expression;

• The expression on the right is evaluated first.
• The resulting value is then stored in the variable on the left.

Examples:
int x;
x = 10; // Assigns 10 to x
x = x + 5; // Assigns 15 to x

Input-Output (I/O) Statements

To perform I/O, you must first include the standard input/output library: #include

printf() - Formatted Output

The printf() function is used to print formatted text and variable values to the console.

Syntax: printf("format_string", argument1, argument2, ...);

The format string contains plain text and format specifiers. Each specifier is a placeholder for an argument.

• %d or %i: for integers (int)
• %f: for float
• %lf: for double (long float)
• %c: for char
• %s: for strings (character arrays)
• \n: special character for a newline.

Example:
int age = 20; float height = 5.8;
printf("Age: %d, Height: %.1f\n", age, height);
Output: Age: 20, Height: 5.8

scanf() - Formatted Input

The scanf() function is used to read formatted data from the user via the keyboard.

Syntax: scanf("format_string", &variable1, &variable2, ...);

Example:
int number;
printf("Enter a number: ");
scanf("%d", &number);

Example Program (Unit 1)

This program demonstrates all concepts from Unit 1 by implementing Practical #1b (Area of a rectangle).

#include <stdio.h> // For printf() and scanf()  int main() { // Declaration Statements  float length, width; float area; // Input Statement (printf for prompt)  printf("Enter the length of the rectangle: "); // Input Statement (scanf to read data)  scanf("%f", &length); printf("Enter the width of the rectangle: "); scanf("%f", &width); // Arithmetic Expression and Assignment Statement  area = length * width; // Output Statement  printf("The area of the rectangle is: %.2f\n", area); return 0; } 

Unit 1: Exam Quick Tips