C Programming Documentation

What is C Programming?

C is a general-purpose programming language created by Dennis Ritchie at Bell Laboratories in 1972. It is a structured, procedural language that has influenced many other programming languages and is still widely used today for system programming, embedded systems, and application development.

History of C

• 1972: C was developed by Dennis Ritchie at Bell Labs
• 1978: Brian Kernighan and Dennis Ritchie published "The C Programming Language" (K&R C)
• 1989: ANSI C standard (X3.159-1989) was published
• 1999: ISO C standard (C99) was published
• 2011: ISO C standard (C11) was published
• 2018: ISO C standard (C18) was published

Features of C

• Fast and Efficient: C programs are known for their speed and efficiency
• Close to Hardware: Provides low-level access to memory and system resources
• Portable: C code can be compiled on various platforms with minimal changes
• Extensible: Rich set of libraries and functions
• Structured: Supports structured programming concepts
• Flexible: Can be used for both low-level and high-level programming

Applications of C

• Operating Systems (Unix, Linux, Windows)
• Embedded Systems
• Database Systems
• Game Development
• Scientific Computing
• Network Drivers
• Robotics

Setting Up C Development Environment

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# Install MinGW-w64 (Minimalist GNU for Windows)
# Download from: https://www.mingw-w64.org/downloads/

# Add MinGW-w64 bin directory to PATH
# Example: C:\mingw64\bin

# Verify installation
gcc --version

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# Install GCC (GNU Compiler Collection)
sudo apt-get update
sudo apt-get install build-essential

# Verify installation
gcc --version

# Install text editor (optional)
sudo apt-get install vim
sudo apt-get install code

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# Install Xcode Command Line Tools
xcode-select --install

# Install Homebrew (package manager)
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

# Install GCC
brew install gcc

# Verify installation
gcc --version

Your First C Program

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#include <stdio.h>

int main() {
    printf("Hello, World!\n");
    return 0;
}

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# Compile the program
gcc hello.c -o hello

# Run the program
./hello

Data Types in C

C provides several built-in data types to store different kinds of data:

Variables in C

Variables are named storage locations in memory. Before using a variable, you must declare it with its type and optionally initialize it.

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#include <stdio.h>

int main() {
    // Variable declaration and initialization
    int age = 25;
    float salary = 50000.50;
    char grade = 'A';
    double pi = 3.14159265359;

    // Multiple variable declaration
    int x, y, z;
    float a, b;

    // Declaration with initialization
    int count = 0;
    float temperature = 98.6;
    char initial = 'J';

    printf("Age: %d\n", age);
    printf("Salary: %.2f\n", salary);
    printf("Grade: %c\n", grade);
    printf("Pi: %.10f\n", pi);

    return 0;
}

Constants

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#include <stdio.h>

#define PI 3.14159265359
#define MAX_SIZE 100

int main() {
    const int MAX_AGE = 120;
    const float GRAVITY = 9.8;

    float radius = 5.0;
    float area = PI * radius * radius;
    
    printf("Area of circle: %.2f\n", area);
    printf("Maximum age: %d\n", MAX_AGE);
    printf("Gravity constant: %.1f\n", GRAVITY);
    
    return 0;
}

Operators in C

C provides a rich set of operators to manipulate variables and values.

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#include <stdio.h>

int main() {
    int a = 10, b = 3;
    
    // Arithmetic operators
    printf("a + b = %d\n", a + b);
    printf("a - b = %d\n", a - b);
    printf("a * b = %d\n", a * b);
    printf("a / b = %d\n", a / b);
    printf("a %% b = %d\n", a % b);
    
    // Relational operators
    printf("a == b: %d\n", a == b);
    printf("a != b: %d\n", a != b);
    printf("a > b: %d\n", a > b);
    
    // Logical operators
    int x = 1, y = 0;
    printf("x && y: %d\n", x && y);
    printf("x || y: %d\n", x || y);
    printf("!x: %d\n", !x);
    
    // Assignment operators
    a += 5;
    printf("a after += 5: %d\n", a);
    
    // Bitwise operators
    unsigned int p = 60, q = 13;
    printf("p & q: %u\n", p & q);
    printf("p | q: %u\n", p | q);
    
    return 0;
}

Control Structures in C

Control structures determine the flow of execution in a program.

if-else Statements

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#include <stdio.h>

int main() {
    int age = 18;
    
    // Simple if statement
    if (age >= 18) {
        printf("You are eligible to vote.\n");
    }
    
    // if-else statement
    if (age >= 18) {
        printf("You are eligible to vote.\n");
    } else {
        printf("You are not eligible to vote.\n");
    }
    
    // if-else if-else statement
    int score = 85;
    if (score >= 90) {
        printf("Grade: A\n");
    } else if (score >= 80) {
        printf("Grade: B\n");
    } else if (score >= 70) {
        printf("Grade: C\n");
    } else {
        printf("Grade: F\n");
    }
    
    return 0;
}

switch Statement

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#include <stdio.h>

int main() {
    int day = 3;
    
    switch (day) {
        case 1:
            printf("Monday\n");
            break;
        case 2:
            printf("Tuesday\n");
            break;
        case 3:
            printf("Wednesday\n");
            break;
        case 4:
            printf("Thursday\n");
            break;
        case 5:
            printf("Friday\n");
            break;
        case 6:
            printf("Saturday\n");
            break;
        case 7:
            printf("Sunday\n");
            break;
        default:
            printf("Invalid day\n");
    }
    
    return 0;
}

Loops

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#include <stdio.h>

int main() {
    // for loop
    printf("For loop: ");
    for (int i = 1; i <= 5; i++) {
        printf("%d ", i);
    }
    printf("\n");
    
    // while loop
    printf("While loop: ");
    int j = 1;
    while (j <= 5) {
        printf("%d ", j);
        j++;
    }
    printf("\n");
    
    // do-while loop
    printf("Do-while loop: ");
    int k = 1;
    do {
        printf("%d ", k);
        k++;
    } while (k <= 5);
    printf("\n");
    
    // Loop control statements
    printf("Loop with break and continue: ");
    for (int i = 1; i <= 10; i++) {
        if (i == 5) continue;
        if (i == 8) break;
        printf("%d ", i);
    }
    printf("\n");
    
    return 0;
}

Functions in C

Functions are blocks of code that perform specific tasks and help in code organization and reuse.

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#include <stdio.h>

// Function declaration (prototype)
int add(int a, int b);
void greet();

// Function definition
int add(int a, int b) {
    return a + b;
}

void greet() {
    printf("Hello, World!\n");
}

// Function with no return value and parameters
void printDetails(char name[], int age) {
    printf("Name: %s\n", name);
    printf("Age: %d\n", age);
}

// Recursive function
int factorial(int n) {
    if (n <= 1) return 1;
    return n * factorial(n - 1);
}

int main() {
    // Calling functions
    greet();
    
    int sum = add(5, 3);
    printf("Sum: %d\n", sum);
    
    printDetails("John", 25);
    
    int fact = factorial(5);
    printf("Factorial of 5: %d\n", fact);
    
    return 0;
}

Function Parameters and Return Types

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#include <stdio.h>

// Different return types
float calculateArea(float radius) {
    return 3.14159 * radius * radius;
}

void swap(int *a, int *b) {
    int temp = *a;
    *a = *b;
    *b = temp;
}

int main() {
    float radius = 5.0;
    float area = calculateArea(radius);
    printf("Area: %.2f\n", area);
    
    int x = 10, y = 20;
    printf("Before swap: x=%d, y=%d\n", x, y);
    swap(&x, &y);
    printf("After swap: x=%d, y=%d\n", x, y);
    
    return 0;
}

Arrays in C

Arrays are collections of elements of the same data type stored in contiguous memory locations.

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#include <stdio.h>

int main() {
    // One-dimensional array
    int numbers[5] = {1, 2, 3, 4, 5};
    
    printf("Array elements: ");
    for (int i = 0; i < 5; i++) {
        printf("%d ", numbers[i]);
    }
    printf("\n");
    
    // Two-dimensional array
    int matrix[2][3] = {
        {1, 2, 3},
        {4, 5, 6}
    };
    
    printf("2D Array:\n");
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 3; j++) {
            printf("%d ", matrix[i][j]);
        }
        printf("\n");
    }
    
    return 0;
}

Strings in C

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#include <stdio.h>
#include <string.h>

int main() {
    // String declaration
    char greeting[] = "Hello, World!";
    char name[50];
    
    // String functions
    printf("String: %s\n", greeting);
    printf("Length: %zu\n", strlen(greeting));
    
    // String copy
    strcpy(name, "John Doe");
    printf("Name: %s\n", name);
    
    // String concatenation
    strcat(name, " - Programmer");
    printf("Full name: %s\n", name);
    
    // String comparison
    char str1[] = "apple";
    char str2[] = "banana";
    
    if (strcmp(str1, str2) < 0) {
        printf("%s comes before %s\n", str1, str2);
    } else {
        printf("%s comes after %s\n", str1, str2);
    }
    
    return 0;
}

Pointers in C

Pointers are variables that store memory addresses of other variables.

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#include <stdio.h>

int main() {
    int num = 10;
    int *ptr = #
    
    printf("Value of num: %d\n", num);
    printf("Address of num: %p\n", &num);
    printf("Value of ptr: %p\n", ptr);
    printf("Value pointed by ptr: %d\n", *ptr);
    
    // Modifying value through pointer
    *ptr = 20;
    printf("New value of num: %d\n", num);
    
    // Pointer arithmetic
    int arr[5] = {10, 20, 30, 40, 50};
    int *arrPtr = arr;
    
    printf("Array elements using pointer: ");
    for (int i = 0; i < 5; i++) {
        printf("%d ", *(arrPtr + i));
    }
    printf("\n");
    
    return 0;
}

Pointers and Functions

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#include <stdio.h>

void swap(int *a, int *b) {
    int temp = *a;
    *a = *b;
    *b = temp;
}

void printArray(int *arr, int size) {
    for (int i = 0; i < size; i++) {
        printf("%d ", *(arr + i));
    }
    printf("\n");
}

int main() {
    int x = 10, y = 20;
    printf("Before swap: x=%d, y=%d\n", x, y);
    swap(&x, &y);
    printf("After swap: x=%d, y=%d\n", x, y);
    
    int numbers[] = {1, 2, 3, 4, 5};
    printf("Array: ");
    printArray(numbers, 5);
    
    return 0;
}

Structures in C

Structures allow you to combine data items of different kinds.

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#include <stdio.h>
#include <string.h>

// Structure definition
struct Person {
    char name[50];
    int age;
    float height;
};

// typedef with structure
typedef struct {
    char street[100];
    char city[50];
    int zip;
} Address;

int main() {
    // Structure variable declaration and initialization
    struct Person person1;
    strcpy(person1.name, "John Doe");
    person1.age = 25;
    person1.height = 5.8;
    
    printf("Person: %s, %d years, %.1f feet\n", 
           person1.name, person1.age, person1.height);
    
    // Structure pointer
    struct Person *personPtr = &person1;
    printf("Using pointer: %s\n", personPtr->name);
    
    // Array of structures
    struct Person people[3] = {
        {"Alice", 30, 5.6},
        {"Bob", 35, 5.9},
        {"Charlie", 28, 5.7}
    };
    
    printf("\nPeople array:\n");
    for (int i = 0; i < 3; i++) {
        printf("%s, %d years\n", people[i].name, people[i].age);
    }
    
    return 0;
}

Unions in C

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#include <stdio.h>
#include <string.h>

union Data {
    int i;
    float f;
    char str[20];
};

int main() {
    union Data data;
    
    data.i = 10;
    printf("data.i: %d\n", data.i);
    
    data.f = 3.14;
    printf("data.f: %.2f\n", data.f);
    
    strcpy(data.str, "Hello");
    printf("data.str: %s\n", data.str);
    
    printf("Size of union: %zu bytes\n", sizeof(union Data));
    
    return 0;
}

File Handling in C

C provides functions for reading from and writing to files.

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#include <stdio.h>

int main() {
    FILE *file;
    char buffer[100];
    
    // Writing to a file
    file = fopen("example.txt", "w");
    if (file == NULL) {
        printf("Error opening file for writing!\n");
        return 1;
    }
    
    fprintf(file, "Hello, File Handling!\n");
    fprintf(file, "This is a test file.\n");
    fclose(file);
    
    // Reading from a file
    file = fopen("example.txt", "r");
    if (file == NULL) {
        printf("Error opening file for reading!\n");
        return 1;
    }
    
    printf("File contents:\n");
    while (fgets(buffer, sizeof(buffer), file) != NULL) {
        printf("%s", buffer);
    }
    fclose(file);
    
    return 0;
}

Binary File Operations

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#include <stdio.h>

struct Student {
    int id;
    char name[50];
    float marks;
};

int main() {
    struct Student students[3] = {
        {1, "Alice", 85.5},
        {2, "Bob", 92.0},
        {3, "Charlie", 78.5}
    };
    
    FILE *file;
    
    // Write binary data
    file = fopen("students.dat", "wb");
    if (file != NULL) {
        fwrite(students, sizeof(struct Student), 3, file);
        fclose(file);
    }
    
    // Read binary data
    struct Student readStudents[3];
    file = fopen("students.dat", "rb");
    if (file != NULL) {
        fread(readStudents, sizeof(struct Student), 3, file);
        fclose(file);
        
        printf("Student data:\n");
        for (int i = 0; i < 3; i++) {
            printf("ID: %d, Name: %s, Marks: %.1f\n",
                   readStudents[i].id, readStudents[i].name, readStudents[i].marks);
        }
    }
    
    return 0;
}

Dynamic Memory Allocation

C provides functions for dynamic memory allocation and deallocation.

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#include <stdio.h>
#include <stdlib.h>

int main() {
    int *ptr;
    int n;
    
    printf("Enter number of elements: ");
    scanf("%d", &n);
    
    // Memory allocation using malloc
    ptr = (int*)malloc(n * sizeof(int));
    
    if (ptr == NULL) {
        printf("Memory allocation failed!\n");
        return 1;
    }
    
    // Store values in allocated memory
    for (int i = 0; i < n; i++) {
        ptr[i] = i + 1;
    }
    
    // Print the values
    printf("Array elements: ");
    for (int i = 0; i < n; i++) {
        printf("%d ", ptr[i]);
    }
    printf("\n");
    
    // Free allocated memory
    free(ptr);
    
    // Using calloc (initializes to zero)
    int *ptr2 = (int*)calloc(5, sizeof(int));
    printf("Calloc initialized array: ");
    for (int i = 0; i < 5; i++) {
        printf("%d ", ptr2[i]);
    }
    printf("\n");
    
    // Using realloc
    ptr2 = (int*)realloc(ptr2, 10 * sizeof(int));
    for (int i = 5; i < 10; i++) {
        ptr2[i] = i + 1;
    }
    
    printf("After realloc: ");
    for (int i = 0; i < 10; i++) {
        printf("%d ", ptr2[i]);
    }
    printf("\n");
    
    free(ptr2);
    
    return 0;
}

Memory Management Best Practices

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#include <stdio.h>
#include <stdlib.h>

void safeMemoryAllocation() {
    int *ptr = NULL;
    
    // Always check if allocation was successful
    ptr = (int*)malloc(5 * sizeof(int));
    if (ptr == NULL) {
        printf("Memory allocation failed!\n");
        return;
    }
    
    // Use the allocated memory
    for (int i = 0; i < 5; i++) {
        ptr[i] = (i + 1) * 10;
    }
    
    // Print values
    for (int i = 0; i < 5; i++) {
        printf("%d ", ptr[i]);
    }
    printf("\n");
    
    // Free memory and set pointer to NULL
    free(ptr);
    ptr = NULL;
}

int main() {
    safeMemoryAllocation();
    return 0;
}