C Basics

• C is a general-purpose computer programming language.
• It was created in the 1970s by Dennis Ritchie, and remains very widely used and influential.

Key Points

• Structured Language: C is a structured programming language, allowing developers to write clear, organized, and efficient code.
• Low-Level and High-Level: It provides both low-level memory manipulation and high-level abstraction for creating a wide range of software.
• Portable: Code written in C is highly portable, meaning it can run on different platforms with minimal modification.
• Extensive Standard Library: C comes with a rich standard library that simplifies common programming tasks.

Structure of a Basic C Program

1#include <stdio.h>
2intmain() {
3// Program logic goes here
4return 0;
5}

Writing and Executing the First C Program

1#include <stdio.h>
2intmain() {
3printf("Hello, World!\n");
4return 0;
5}

• To execute the program, save it to a file with a .c extension (e.g., hello.c), and then compile and run it using a C compiler like gcc:gcc hello.c -o hello./hello
• This code prints "Hello, World!" to the console.

C Character Set

• In C, a character set is the collection of characters that are recognized by the language.
• The basic character set in C includes letters (both uppercase and lowercase), digits, and a few special characters like punctuation symbols. Here's a simple example that uses characters:

1#include <stdio.h>
2
3int main() {
4    char firstLetter = 'A';
5    char secondLetter = 'B';
6
7    printf("First letter: %c\n", firstLetter);
8    printf("Second letter: %c\n", secondLetter);
9
10    return 0;
11}
12

Identifiers and Keywords

• Identifiers in C are names given to various program elements such as variables, functions, and arrays.
• They must start with a letter or an underscore and can be followed by letters, digits, or underscores. C also has a set of keywords, which are reserved words with predefined meanings.

1include <stdio.h>
2
3int main() {
4    int number = 42; // 'number' is an identifier
5    if (number > 0) {
6        printf("The number is positive.\n"); // 'if' is a keyword
7    } else {
8        printf("The number is non-positive.\n"); // 'else' is a keyword
9    }
10
11    return 0;
12}
13

Data Types

• Data types in C specify the type of data a variable can hold.
• Common data types include int, char, float, and double. Here's an example using different data types:

1#include <stdio.h>
2
3int main() 
4{
5    int age = 25;
6    char grade = 'A';
7    float price = 12.99;
8    double pi = 3.14159265359;
9
10    printf("Age: %d\n", age);
11    printf("Grade: %c\n", grade);
12    printf("Price: %.2f\n", price);
13    printf("Pi: %.10lf\n", pi);
14
15    return 0;
16}
17

Constants

• Constants are fixed values in C.
• They can be of various types, including integer constants, floating-point constants, and character constants.
• Here's an example with integer and character constants:

1#include <stdio.h>
2
3int main() 
4{
5    const int numberOfMonths = 12; // Integer constant
6    const char firstLetter = 'A'; // Character constant
7
8    printf("Number of months in the year: %d\n", numberOfMonths);
9printf("First letter of the alphabet: %c\n", FirstLetter);
10    return 0;
11}
12

Symbolic Constants

• Symbolic constants are user-defined constants represented by identifiers.
• They are typically created using the #define preprocessor directive.

1#include <stdio.h>
2
3#define PI 3.14159265359
4
5int main()
6{
7    double radius = 5.0;
8    double area = PI * radius * radius;
9
10    printf("The area of the circle: %.2lf\n", area);
11
12    return 0;
13}
14

Variable Declarations

• Variable declarations specify the data type and name of a variable.

1#include <stdio.h>
2
3int main() {
4    int x; // Variable declaration
5
6    x = 10; // Variable initialization
7
8    printf("The value of x: %d\n", x);
9
10    return 0;
11}
12

#include Preprocessor Directive

• The #include directive is used to include header files in a C program.
• It allows you to use functions and features defined in those header files. For example:

1#include <stdio.h>
2
3intmain() {
4// Code that uses functions from the 'stdio.h' header
5return 0;
6}
7
8

Expression Statements

1#include <stdio.h>
2
3intmain()
4{
5int a = 5;
6int b = 3;
7int sum = a + b; // Expression statement
8printf("The sum of %d and %d is %d\n", a, b, sum);
9return 0;
10}

Compound Statements

• Compound statements, also known as blocks, are enclosed within curly braces {} and can contain multiple statements.
• They are often used for grouping statements together.

1#include <stdio.h>
2int main() 
3{
4int x = 10;
5int y = 5;
6if (x > y) 
7{
8printf("x is greater than y.\n");
9} 
10  
11else 
12{
13printf("x is not greater than y.\n");
14}
15  
16return 0;
17}

Conclusion