C Programming: Notes & Examples

Why learn C

C gives deep control over memory and performance. It is foundational for operating systems, embedded software, compilers, and performance-critical libraries.

Learning C builds strong low-level reasoning that helps with C++, Rust, systems programming, and interview problem solving.

Basic C program structure

#include <stdio.h>

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

Primitive data types

• int for whole numbers.
• float and double for decimal values.
• char for single characters.
• Use sizeof(type) to inspect memory footprint.

Operators in C

#include <stdio.h>

int main(void) {
    int a = 10, b = 3;
    printf("Sum: %d\n", a + b);
    printf("Remainder: %d\n", a % b);
    printf("a > b: %d\n", a > b);
    return 0;
}

if-else and switch

Control statements drive branching logic. Use switch when comparing one variable against multiple discrete values.

int marks = 82;
if (marks >= 90) {
    printf("Grade A\n");
} else if (marks >= 75) {
    printf("Grade B\n");
} else {
    printf("Grade C\n");
}

for, while, and do-while

• for is best when iteration count is known.
• while suits condition-driven loops.
• do-while runs at least once.

for (int i = 0; i < 3; i++) {
    printf("for: %d\n", i);
}

int count = 0;
while (count < 3) {
    printf("while: %d\n", count);
    count++;
}

Function declarations and definitions

C uses function prototypes to declare signatures before use. This helps the compiler validate argument and return types.

#include <stdio.h>

int add(int a, int b); // prototype

int main(void) {
    printf("%d\n", add(4, 5));
    return 0;
}

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

Pass by value understanding

• C passes arguments by value by default.
• Use pointers when a function must modify caller data.
• Keep function responsibilities narrow and testable.

Addresses and dereferencing

Pointers store memory addresses. The '&' operator gets an address and '*' dereferences it to access the value at that address.

#include <stdio.h>

int main(void) {
    int value = 25;
    int *ptr = &value;

    printf("value=%d\n", value);
    printf("address=%p\n", (void*)ptr);
    printf("dereference=%d\n", *ptr);
    return 0;
}

Pointer safety tips

• Initialize pointers before dereferencing.
• Avoid returning pointers to local stack variables.
• Set freed pointers to NULL to reduce accidental reuse.

Array fundamentals

• Arrays store same-type elements contiguously.
• Indexes start at 0.
• Bounds checking is manual in C.

String handling with char arrays

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

int main(void) {
    int scores[3] = {78, 85, 92};
    char name[20] = "Rishtaara";

    printf("First score: %d\n", scores[0]);
    printf("Name length: %zu\n", strlen(name));
    return 0;
}

Using struct for domain modeling

Structures let you group related fields under one custom type. They are key for representing records like students, employees, and products.

#include <stdio.h>

struct Student {
    char name[30];
    int grade;
    float marks;
};

int main(void) {
    struct Student s = {"Ishita", 12, 91.5f};
    printf("%s scored %.1f\n", s.name, s.marks);
    return 0;
}

typedef and nested structs

• typedef improves readability for custom types.
• Structs can contain other structs.
• Combine structs with pointers for dynamic data models.

Project outcome

• Capture student details with structs.
• Store multiple records in arrays.
• Search and print records by criteria.
• Practice modular function design.

Starter project code

#include <stdio.h>

typedef struct {
    int id;
    char name[40];
    float marks;
} Student;

int main(void) {
    Student students[2] = {
        {1, "Asha", 88.5f},
        {2, "Kabir", 91.0f}
    };

    for (int i = 0; i < 2; i++) {
        printf("%d %s %.1f\n", students[i].id, students[i].name, students[i].marks);
    }
    return 0;
}