Programming Fundamentals Using C — Complete Notes

Introduction to C Programming

C is a general-purpose, procedural programming language developed by Dennis Ritchie at Bell Labs in 1972. It is called the "mother of all languages" because most modern languages (C++, Java, Python) are influenced by C.

Why C?

• Closest to hardware — gives direct memory control
• Fast execution speed
• Foundation for operating systems (Linux, Windows kernel)
• Teaches how computers actually work

Structure of a C Program:

#include <stdio.h>    // Header file

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

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Data Types and Variables

Basic Data Types:

| Type | Size | Range | Example | |---|---|---|---| | int | 4 bytes | -2,147,483,648 to 2,147,483,647 | int age = 20; | | float | 4 bytes | ~6 decimal digits | float pi = 3.14; | | double | 8 bytes | ~15 decimal digits | double x = 3.14159; | | char | 1 byte | -128 to 127 | char grade = 'A'; |

Format Specifiers: %d (int), %f (float), %lf (double), %c (char), %s (string)

Variable Declaration Rules:

• Must start with letter or underscore
• Cannot use keywords (int, while, for)
• Case-sensitive (age ≠ Age)

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Operators

| Category | Operators | |---|---| | Arithmetic | + - * / % | | Relational | == != > < >= <= | | Logical | && (AND), || (OR), ! (NOT) | | Assignment | = += -= *= /= | | Bitwise | & | ^ ~ << >> | | Increment/Decrement | ++ -- |

Operator Precedence (High to Low): (), ++ --, * / %, + -, relational, logical, assignment

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Control Flow

if-else

if (marks >= 60) {
    printf("Pass");
} else if (marks >= 40) {
    printf("Compartment");
} else {
    printf("Fail");
}

switch

switch(day) {
    case 1: printf("Monday"); break;
    case 2: printf("Tuesday"); break;
    default: printf("Invalid");
}

Loops

// for loop
for (int i = 0; i < 5; i++) { printf("%d ", i); }

// while loop
int i = 0;
while (i < 5) { printf("%d ", i); i++; }

// do-while (executes at least once)
do { printf("%d ", i); i++; } while (i < 5);

break — exits the loop immediately continue — skips current iteration, goes to next

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Functions

A function is a reusable block of code that performs a specific task.

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

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

int main() {
    int result = add(5, 3);  // Function call
    printf("%d", result);    // Output: 8
    return 0;
}

Types of Function Arguments:

• Call by Value — copy passed; original not changed
• Call by Reference — address (pointer) passed; original can be changed

Recursion: Function calling itself.

int factorial(int n) {
    if (n == 0) return 1;
    return n * factorial(n - 1);
}
// factorial(5) = 5*4*3*2*1 = 120

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Arrays

An array stores multiple values of the same type.

int marks[5] = {85, 90, 78, 92, 88};
// Access: marks[0]=85, marks[4]=88

// 2D Array (Matrix)
int matrix[3][3] = {1,2,3},{4,5,6},{7,8,9};

String (char array):

char name[20] = "WohoTech";
printf("%s", name);         // Output: WohoTech
printf("%d", strlen(name)); // Output: 8

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Pointers

A pointer stores the memory address of another variable.

int x = 10;
int *p = &x;     // p holds address of x

printf("%d", x);   // 10 (value)
printf("%p", p);   // 0x7fff... (address)
printf("%d", *p);  // 10 (value at address — dereferencing)

*p = 20;           // Changes x to 20 through pointer

Pointer Arithmetic:

int arr[] = {10, 20, 30};
int *p = arr;
printf("%d", *p);     // 10
printf("%d", *(p+1)); // 20
printf("%d", *(p+2)); // 30

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Structures

A structure groups different data types under one name.

struct Student {
    char name[50];
    int rollno;
    float cgpa;
};

struct Student s1;
strcpy(s1.name, "Rahul");
s1.rollno = 101;
s1.cgpa = 8.5;

printf("%s scored %.1f", s1.name, s1.cgpa);

typedef — creates alias for structure:

typedef struct { char name[50]; int age; } Person;
Person p1;

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Solved PYQ Questions

Q1 (2023): Write a C program to find factorial using recursion.

#include <stdio.h>
int factorial(int n) {
    if (n <= 1) return 1;
    return n * factorial(n-1);
}
int main() {
    int n;
    printf("Enter n: "); scanf("%d", &n);
    printf("Factorial = %d", factorial(n));
    return 0;
}

Q2 (2023): What is the output?

int x = 5;
printf("%d %d", x++, ++x);

Answer: Output depends on compiler evaluation order. Post-increment (x++) uses current value then increments; pre-increment (++x) increments first.

Q3 (2022): Difference between array and pointer. Array is a fixed-size collection; pointer is a variable storing an address. Array name acts as a constant pointer to its first element, but you cannot reassign an array name.

Q4 (2022): Write program to reverse a string without library function.

void reverse(char str[]) {
    int n = strlen(str);
    for (int i = 0; i < n/2; i++) {
        char temp = str[i];
        str[i] = str[n-1-i];
        str[n-1-i] = temp;
    }
}

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Exam Revision Checklist

• Data types: int(4B), float(4B), double(8B), char(1B)
• Difference between call by value and call by reference
• Recursion: base case is mandatory to prevent infinite recursion
• Array indexing starts from 0
• Pointer: * for declaration and dereferencing, & for address-of
• Structure vs Union: structure gives each member own memory; union shares memory
• String functions: strlen, strcpy, strcat, strcmp