C Programming Course — Mayank Basena

01

Hello World & Setup

Your first C program. Every program starts at main().

#include <stdio.h>

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

// Compile: gcc hello.c -o hello
// Run: ./hello

02

Variables & Data Types

int, float, char, double — boxes that hold different kinds of data.

#include <stdio.h>

int main() {
    int age = 15;
    float height = 5.9;
    char grade = 'A';
    char name[] = "Mayank";
    double pi = 3.14159265;

    printf("Name: %s\n", name);
    printf("Age: %d\n", age);
    printf("Height: %.1f\n", height);
    printf("Grade: %c\n", grade);
    printf("Pi: %.8f\n", pi);
    return 0;
}

03

Operators

Math (+ - * / %), comparison (== != > <), logical (&& || !), bitwise (& | ^).

#include <stdio.h>

int main() {
    int a = 10, b = 3;
    printf("%d + %d = %d\n", a, b, a + b);
    printf("%d / %d = %d\n", a, b, a / b);
    printf("%d %% %d = %d\n", a, b, a % b);
    printf("%d == %d => %d\n", a, b, a == b);
    printf("5 & 3 = %d\n", 5 & 3);
    printf("5 | 3 = %d\n", 5 | 3);
    printf("5 ^ 3 = %d\n", 5 ^ 3);
    printf("1 << 3 = %d\n", 1 << 3);
    return 0;
}

04

If/Else & Switch

Make choices. If it rains, take an umbrella. Switch is a vending machine.

#include <stdio.h>

int main() {
    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");

    int day = 3;
    switch (day) {
        case 1: printf("Monday\n"); break;
        case 2: printf("Tuesday\n"); break;
        case 3: printf("Wednesday\n"); break;
        default: printf("Other day\n"); break;
    }
    return 0;
}

05

Loops

Repeat things. for runs N times. while runs until false. do-while runs at least once.

#include <stdio.h>

int main() {
    for (int i = 0; i < 5; i++) printf("for: %d\n", i);

    int n = 0;
    while (n < 5) { printf("while: %d\n", n); n++; }

    int m = 0;
    do { printf("do-while: %d\n", m); m++; } while (m < 5);

    for (int i = 1; i <= 10; i++) {
        if (i % 2 == 0) continue;
        printf("odd: %d\n", i);
    }
    return 0;
}

06

Functions

Recipes for code. Give ingredients (params), get result (return).

#include <stdio.h>

int add(int a, int b) { return a + b; }
float area(float r) { return 3.14159 * r * r; }
int fact(int n) { return n <= 1 ? 1 : n * fact(n-1); }
void greet(char name[]) { printf("Hello, %s!\n", name); }

int main() {
    printf("5+3=%d\n", add(5,3));
    printf("area(5)=%.2f\n", area(5));
    printf("5!=%d\n", fact(5));
    greet("Mayank");
    return 0;
}

07

Arrays

A row of boxes, same type. Box 0 is first, box 1 is second (index starts at 0).

#include <stdio.h>

int main() {
    int nums[5] = {10, 20, 30, 40, 50};
    for (int i = 0; i < 5; i++) printf("%d ", nums[i]);
    printf("\n");

    int matrix[3][3] = {{1,2,3},{4,5,6},{7,8,9}};
    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 3; j++) printf("%3d", matrix[i][j]);
        printf("\n");
    }
    return 0;
}

08

Strings

Arrays of chars ending with \0. Use string.h for strlen, strcpy, strcat, strcmp.

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

int main() {
    char s[50] = "Hello";
    printf("len=%zu\n", strlen(s));
    strcat(s, " World");
    printf("%s\n", s);
    printf("cmp=%d\n", strcmp("abc","abd"));
    char *p = strchr(s, 'W');
    if (p) printf("found at %ld\n", p-s);
    return 0;
}

09

Structs & Enums

Group related data together. Struct is a custom box. Enum is a named list of choices.

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

struct Person {
    char name[50];
    int age;
    float gpa;
};

enum Color { RED, GREEN, BLUE };

void print_person(struct Person p) {
    printf("%s (age %d) gpa=%.1f\n", p.name, p.age, p.gpa);
}

int main() {
    struct Person me;
    strcpy(me.name, "Mayank");
    me.age = 15;
    me.gpa = 9.5;
    print_person(me);

    enum Color c = GREEN;
    printf("Color: %d\n", c);
    return 0;
}

10

Dynamic Memory

malloc gives you memory. free gives it back. Use it or leak it.

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

int main() {
    int *arr = malloc(5 * sizeof(int));
    if (!arr) return 1;
    for (int i = 0; i < 5; i++) arr[i] = (i+1) * 10;
    for (int i = 0; i < 5; i++) printf("%d ", arr[i]);
    printf("\n");
    free(arr);

    int *big = realloc(arr, 10 * sizeof(int));
    if (big) { arr = big; }
    return 0;
}

11

Pointers

A pointer holds an address — where something lives in memory. Like a treasure map.

#include <stdio.h>

int main() {
    int x = 42;
    int *p = &x;
    printf("x=%d addr=%p *p=%d\n", x, (void*)p, *p);
    *p = 100;
    printf("x now=%d\n", x);

    int arr[] = {10,20,30};
    int *ap = arr;
    for (int i = 0; i < 3; i++) printf("%d ", *(ap+i));
    printf("\n");
    return 0;
}

12

Pointer Arithmetic

Move through memory. p+1 moves to next int, not next byte.

#include <stdio.h>

int main() {
    int arr[] = {10, 20, 30, 40, 50};
    int *p = arr;

    printf("*p = %d\n", *p);
    printf("*(p+1) = %d\n", *(p+1));
    printf("*(p+2) = %d\n", *(p+2));

    p += 3;
    printf("after p+=3: %d\n", *p);

    int *start = &arr[0];
    int *end = &arr[4];
    printf("distance: %ld ints\n", end - start);
    return 0;
}

13

Function Pointers

Pass functions as arguments. A pointer that points to code, not data.

#include <stdio.h>

int add(int a, int b) { return a + b; }
int sub(int a, int b) { return a - b; }
int mul(int a, int b) { return a * b; }

void calc(int (*op)(int,int), int a, int b) {
    printf("result: %d\n", op(a, b));
}

int main() {
    calc(add, 10, 5);
    calc(sub, 10, 5);
    calc(mul, 10, 5);

    int (*ops[3])(int,int) = {add, sub, mul};
    for (int i = 0; i < 3; i++) printf("%d\n", ops[i](10,5));
    return 0;
}

14

File I/O

Read and write files. fopen opens, fclose closes, fprintf writes, fgets reads.

#include <stdio.h>

int main() {
    FILE *f = fopen("test.txt", "w");
    fprintf(f, "Hello File!\n");
    fprintf(f, "Line 2: %d\n", 42);
    fclose(f);

    f = fopen("test.txt", "r");
    char buf[256];
    while (fgets(buf, sizeof(buf), f)) printf("%s", buf);
    fclose(f);
    return 0;
}

15

Preprocessor

#include, #define, #ifdef — things that happen before compilation.

#include <stdio.h>

#define PI 3.14159
#define SQUARE(x) ((x)*(x))
#define MAX(a,b) ((a)>(b)?(a):(b))

#ifdef DEBUG
#define LOG(msg) printf("DEBUG: %s\n", msg)
#else
#define LOG(msg)
#endif

int main() {
    printf("PI=%f\n", PI);
    printf("5^2=%d\n", SQUARE(5));
    printf("max(3,7)=%d\n", MAX(3,7));
    LOG("testing");
    return 0;
}

16

Bit Fields & Unions

Pack bits tight. Unions share memory between different types.

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

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

struct Flags {
    unsigned int bold : 1;
    unsigned int italic : 1;
    unsigned int underline : 1;
    unsigned int size : 5;
};

int main() {
    union Data d;
    d.i = 42;
    printf("int: %d\n", d.i);
    d.f = 3.14;
    printf("float: %f (int was: %d)\n", d.f, d.i);

    struct Flags f = {1, 0, 1, 14};
    printf("bold=%d italic=%d underline=%d size=%d\n",
           f.bold, f.italic, f.underline, f.size);
    return 0;
}

17

Linked Lists

Each node points to the next. Like a treasure hunt where each clue leads to the next.

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

struct Node { int data; struct Node *next; };

void push(struct Node **head, int val) {
    struct Node *n = malloc(sizeof(struct Node));
    n->data = val;
    n->next = *head;
    *head = n;
}

void print(struct Node *head) {
    while (head) { printf("%d -> ", head->data); head = head->next; }
    printf("NULL\n");
}

void free_list(struct Node *head) {
    while (head) { struct Node *t = head; head = head->next; free(t); }
}

int main() {
    struct Node *list = NULL;
    push(&list, 30); push(&list, 20); push(&list, 10);
    print(list);
    free_list(list);
    return 0;
}

18

Build Systems & Projects

Makefiles, header files, multi-file projects. How real C projects are built.

# project structure:
# src/main.c  src/utils.c  include/utils.h
# Makefile

# Makefile example:
CC = gcc
CFLAGS = -Wall -Iinclude
SRCS = src/main.c src/utils.c
OBJS = $(SRCS:.c=.o)
TARGET = app

all: $(TARGET)

$(TARGET): $(OBJS)
	$(CC) $(OBJS) -o $(TARGET)

src/%.o: src/%.c
	$(CC) $(CFLAGS) -c $< -o $@

clean:
	rm -f $(OBJS) $(TARGET)

# utils.h:
#ifndef UTILS_H
#define UTILS_H
int add(int a, int b);
void print_array(int *arr, int len);
#endif