Unit 1: Basics, Algorithm & Operators ( Programming in C Language)

1️⃣ Explain Algorithm with Example and Properties.

Definition:
Algorithm is a step-by-step procedure to solve a problem in a finite number of steps.

Example: Add two numbers

1. Start

2. Read two numbers, A and B

3. Calculate Sum = A + B

4. Print Sum

5. Stop

Properties of a good algorithm:

• Input: Accepts zero or more inputs

• Output: Produces at least one output

• Definiteness: Steps are clear and unambiguous

• Finiteness: Algorithm must terminate after finite steps

• Effectiveness: Steps are basic, feasible, and solvable manually or by machine

---

2️⃣ Draw Flowchart and Explain Sum of First 10 Numbers

Flowchart:

   ┌───────┐
   │ Start │
   └───┬───┘
       ↓
   i=1, sum=0
       ↓
 ┌── i ≤ 10 ? ──┐
 │ Yes        No│
 ↓             ↓
sum=sum+i     Print sum
i=i+1         ↓
 │          ┌───────┐
 └─────────► Stop  │
             └─────┘

Explanation:

• Initialize i=1 and sum=0.

• Check condition i ≤ 10.

• Add i to sum and increment i.

• Repeat until i > 10.

• Print final sum and stop.

---

3️⃣ Explain Compilation & Execution Process in C

Steps:

1. Editing: Write source code in .c file.

2. Preprocessing: Removes comments, expands macros, includes header files.

3. Compilation: Converts source code to assembly code.

4. Assembly: Converts assembly code into object code (.o file).

5. Linking: Combines object code with libraries to produce executable.

6. Execution: OS loads and runs the executable file.

Example:

#include <stdio.h>
int main() {
    printf("Hello, World!");
    return 0;
}

---

4️⃣ Explain Keywords, Identifiers, and Constants in C

Keywords: Reserved words in C with predefined meaning.
Example: int, float, if, else, return

Identifiers: User-defined names for variables, functions, arrays, etc.
Example: sum, age, myFunction

Constants: Fixed values that do not change.
Example: #define PI 3.14 or const int x = 5;

Difference between Keywords and Identifiers:

Keywords	Identifiers
Reserved by C	User-defined names
Cannot be used as variable names	Can be used as variable or function names
Example: int, float	Example: sum, age

---

5️⃣ Explain Operators in C with Examples

Types of operators:

1. Arithmetic: + - * / %

2. Unary: ++ --

3. Relational/Logical: > < == != && || !

4. Bitwise: & | ^ << >>

5. Assignment: = += -= *= /= %=

6. Conditional: ?:

Examples:

int a=5, b=3;
int c;
c = a + b;  // 8
c = a & b;  // 1 (bitwise AND)
c = a << 1; // 10 (left shift)

Precedence & Associativity:

• Precedence decides which operator evaluated first

• Associativity decides order for operators with same precedence

Example:

10 + 20 * 5  // 110, '*' has higher precedence
100 / 10 * 5 // 50, '/' and '*' have same precedence, left-to-right

---

Unit 2: Control Structures, Functions, Arrays

6️⃣ Explain Control Structures in C with Examples

Definition: Control structures manage the flow of execution in a program.

Types:

1. Sequential: Statements executed line by line.

2. Decision Making (Selection): if, if-else, switch-case

3. Loops (Iteration): for, while, do-while

4. Jump Statements: break, continue, goto

Examples:

For Loop (Factorial):

int n=5, i, fact=1;
for(i=1;i<=n;i++) fact*=i;
printf("%d", fact);

While Loop (Even Numbers):

int i=2;
while(i<=10){ printf("%d ",i); i+=2; }

Switch-Case:

int day=3;
switch(day){
  case 1: printf("Mon"); break;
  case 2: printf("Tue"); break;
  default: printf("Other"); 
}

---

7️⃣ Explain Functions in C with Types and Examples

Definition: Block of code that performs a specific task and can be reused.

Advantages: Code reusability, easy debugging, modularity

Types:

• Library functions: printf(), scanf()

• User-defined functions

Categories based on arguments & return type:

1. No arguments, no return:

void hello(){ printf("Hi"); }

2. Arguments, no return:

void sum(int a,int b){ printf("%d",a+b); }

3. No arguments, return value:

int getNum(){ return 10; }

4. Arguments & return:

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

Call by value vs Call by reference:

• Call by value → function gets a copy, original variable not changed

• Call by reference → function gets address, original variable can be changed

---

8️⃣ Explain Arrays in C with Examples

Definition: Array = collection of elements of same type in contiguous memory.

Types:

• 1D Array: int arr[5]={1,2,3,4,5};

• 2D Array: int mat[2][2]={{1,2},{3,4}};

• Multidimensional Array

Example Programs:

Sum of 1D Array:

int arr[5], i, sum=0;
for(i=0;i<5;i++){ scanf("%d",&arr[i]); sum+=arr[i]; }
printf("Sum=%d", sum);

Matrix Addition (2D Array):

int a[2][2], b[2][2], sum[2][2], i,j;
for(i=0;i<2;i++) for(j=0;j<2;j++) scanf("%d",&a[i][j]);
for(i=0;i<2;i++) for(j=0;j<2;j++) scanf("%d",&b[i][j]);
for(i=0;i<2;i++) for(j=0;j<2;j++) sum[i][j]=a[i][j]+b[i][j];
for(i=0;i<2;i++){ for(j=0;j<2;j++) printf("%d ",sum[i][j]); printf("\n"); }

---

9️⃣ Program Based Long Questions

1. Factorial using recursion:

int fact(int n){ if(n<=1) return 1; else return n*fact(n-1);}

2. Sum of first 10 numbers using loop & function:

int sum10(){ int i, sum=0; for(i=1;i<=10;i++) sum+=i; return sum; }

3. Matrix addition program → See 2D array example above.

4. Demonstrate Bitwise Operators:

int a=5,b=3;
printf("%d %d %d %d %d", a&b, a|b, a^b, a<<1, a>>1);

Unit 1 (Programming in C with Data Structures) – Short Notes (6 Marks Type)

 Q1. Define Algorithm and its properties.

Answer:
An algorithm is a step-by-step finite process to solve a specific problem.

Properties:

1. Definiteness → Steps must be clear.

2. Finiteness → Algorithm must end after finite steps.

3. Input → Zero or more inputs accepted.

4. Output → At least one output produced.

5. Effectiveness → Steps must be simple and feasible.

---

Q2. What is a Flowchart? List its advantages.

Answer:
A flowchart is a graphical representation of an algorithm using symbols like oval (Start/End), rectangle (Process), diamond (Decision), parallelogram (I/O).

Advantages:

• Easy to understand.

• Helps in debugging before coding.

• Improves communication between developers.

---

Q3. Explain the structure of a C program.

Answer:
Basic structure:

1. Preprocessor directives (#include <stdio.h>)

2. Main function (int main() { ... })

3. Declarations (variables)

4. Statements (logic/code)

5. Return statement (return 0;)

---

Q4. Explain Compilation & Execution of a C program.

Answer:
Steps:

1. Writing → Save program as .c file.

2. Compilation → Compiler converts C code → machine code.

3. Linking → Connects with libraries.

4. Execution → Run the program → output is shown.

---

Q5. What are Data Types in C?

Answer:
Data types define the kind of data stored in variables.

• Basic: int, float, char, double.

• Derived: arrays, functions, pointers.

• User-defined: structures, union, enum.

• Void: no value.

---

Q6. What are Identifiers and Keywords in C?

Answer:

• Identifiers: Names given to variables, functions, etc. (e.g., marks, sum).

• Keywords: Reserved words with special meaning, cannot be used as identifiers (e.g., int, while, return).

✅ Day 5 Solution - DSA with C

 

✅ 1. Implement your own strlen()

#include <stdio.h>

int my_strlen(char str[]) {
    int i = 0;
    while (str[i] != '\0') {
        i++;
    }
    return i;
}

int main() {
    char str[100];
    printf("Enter a string: ");
    scanf("%s", str);
    printf("Length of string = %d\n", my_strlen(str));
    return 0;
}

---

✅ 2. Implement your own strcpy()

#include <stdio.h>

void my_strcpy(char dest[], char src[]) {
    int i = 0;
    while (src[i] != '\0') {
        dest[i] = src[i];
        i++;
    }
    dest[i] = '\0'; // Null-terminate
}

int main() {
    char src[100], dest[100];
    printf("Enter a string to copy: ");
    scanf("%s", src);

    my_strcpy(dest, src);
    printf("Copied string: %s\n", dest);
    return 0;
}

---

✅ 3. Implement your own strcmp()

#include <stdio.h>

int my_strcmp(char str1[], char str2[]) {
    int i = 0;
    while (str1[i] != '\0' && str2[i] != '\0') {
        if (str1[i] != str2[i])
            return str1[i] - str2[i];
        i++;
    }
    return str1[i] - str2[i]; // Also handles different lengths
}

int main() {
    char str1[100], str2[100];
    printf("Enter two strings:\n");
    scanf("%s %s", str1, str2);

    int result = my_strcmp(str1, str2);
    if (result == 0)
        printf("Strings are equal.\n");
    else if (result < 0)
        printf("First string is smaller.\n");
    else
        printf("First string is greater.\n");

    return 0;
}

---

✅ 4. LeetCode Problem: Valid Anagram

Two strings are anagrams if they contain the same characters in any order.

✨ Custom C Solution:

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

int isAnagram(char s[], char t[]) {
    int count[26] = {0};

    if (strlen(s) != strlen(t))
        return 0;

    for (int i = 0; s[i] != '\0'; i++) {
        count[s[i] - 'a']++;
        count[t[i] - 'a']--;
    }

    for (int i = 0; i < 26; i++) {
        if (count[i] != 0)
            return 0;
    }

    return 1;
}

int main() {
    char s[100], t[100];
    printf("Enter first string: ");
    scanf("%s", s);
    printf("Enter second string: ");
    scanf("%s", t);

    if (isAnagram(s, t))
        printf("Valid Anagram\n");
    else
        printf("Not an Anagram\n");

    return 0;
}

✅ This C code solves the Valid Anagram LeetCode problem without using libraries like sort.

🚀 DSA with C – Day 5: Strings in C

🎯 Goal:

• Understand how strings work in C

• Perform common string operations:

  • Reverse a string

  • Check for palindrome

  • Count character frequency

  • Check if two strings are anagrams

---

🧠 What is a String in C?

A string is a character array ending with a null character (\0).

🔧 Declaration

char str[100]; // Character array

📥 Input

scanf("%s", str); // No spaces
fgets(str, sizeof(str), stdin); // With spaces

---

👨‍💻 1. Reverse a String

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

int main() {
    char str[100];
    printf("Enter a string: ");
    scanf("%s", str); // Use fgets if you want spaces

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

    printf("Reversed string: %s\n", str);
    return 0;
}

---

👨‍💻 2. Check if a String is a Palindrome

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

int main() {
    char str[100];
    int flag = 1;

    printf("Enter a string: ");
    scanf("%s", str);

    int len = strlen(str);
    for (int i = 0; i < len / 2; i++) {
        if (str[i] != str[len - i - 1]) {
            flag = 0;
            break;
        }
    }

    if (flag)
        printf("Palindrome\n");
    else
        printf("Not a palindrome\n");

    return 0;
}

---

👨‍💻 3. Character Frequency Count

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

int main() {
    char str[100];
    int freq[256] = {0}; // ASCII chars

    printf("Enter a string: ");
    scanf("%s", str);

    for (int i = 0; str[i] != '\0'; i++) {
        freq[(int)str[i]]++;
    }

    printf("Character frequencies:\n");
    for (int i = 0; i < 256; i++) {
        if (freq[i] > 0)
            printf("%c: %d\n", i, freq[i]);
    }

    return 0;
}

---

👨‍💻 4. Check if Two Strings Are Anagrams

Two strings are anagrams if they contain the same characters in any order.

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

int isAnagram(char str1[], char str2[]) {
    int count[256] = {0};

    if (strlen(str1) != strlen(str2))
        return 0;

    for (int i = 0; str1[i]; i++) {
        count[(int)str1[i]]++;
        count[(int)str2[i]]--;
    }

    for (int i = 0; i < 256; i++) {
        if (count[i] != 0)
            return 0;
    }

    return 1;
}

int main() {
    char str1[100], str2[100];
    printf("Enter two strings: ");
    scanf("%s %s", str1, str2);

    if (isAnagram(str1, str2))
        printf("Anagram\n");
    else
        printf("Not anagram\n");

    return 0;
}

---

🧪 Practice Problems:

1. Count vowels and consonants in a string.

2. Convert lowercase letters to uppercase.

3. Remove duplicate characters from a string.

4. Check if two strings are rotations of each other (e.g., abc and cab).

---

📘 Homework for Day 5:

• Implement your own versions of:

  • strlen()

  • strcpy()

  • strcmp()

• Try a string problem from LeetCode: Valid Anagram

✅ Day 4 solution - DSA with C

 Find the GCD of Two Numbers Using Recursion

GCD (Greatest Common Divisor) using Euclidean Algorithm:

#include <stdio.h>

int gcd(int a, int b) {
    if (b == 0)
        return a;
    return gcd(b, a % b);
}

int main() {
    int num1, num2;
    printf("Enter two numbers: ");
    scanf("%d %d", &num1, &num2);
    printf("GCD of %d and %d is %d\n", num1, num2, gcd(num1, num2));
    return 0;
}

---

✅ 2. Recursive Function to Calculate Power (xⁿ)

#include <stdio.h>

int power(int x, int n) {
    if (n == 0)
        return 1;
    return x * power(x, n - 1);
}

int main() {
    int base, exponent;
    printf("Enter base and exponent: ");
    scanf("%d %d", &base, &exponent);
    printf("%d^%d = %d\n", base, exponent, power(base, exponent));
    return 0;
}

---

✅ 3. Reverse an Array Using Recursion

#include <stdio.h>

void reverse(int arr[], int start, int end) {
    if (start >= end)
        return;
    
    // Swap
    int temp = arr[start];
    arr[start] = arr[end];
    arr[end] = temp;

    reverse(arr, start + 1, end - 1);
}

int main() {
    int arr[100], n;
    printf("Enter number of elements: ");
    scanf("%d", &n);

    printf("Enter %d elements:\n", n);
    for (int i = 0; i < n; i++)
        scanf("%d", &arr[i]);

    reverse(arr, 0, n - 1);

    printf("Reversed array:\n");
    for (int i = 0; i < n; i++)
        printf("%d ", arr[i]);

    return 0;
}

🚀 DSA with C – Day 4: Recursion + Factorial + Fibonacci + Array Sum

 

🎯 Goal:

• Understand the concept of Recursion

• Write recursive functions for:

  • Factorial

  • Fibonacci series

  • Sum of array elements

• Compare recursion with iteration

---

🧠 What is Recursion?

A function calling itself to solve a smaller version of the same problem.

🔄 Recursion Structure:

return_type function_name(parameters) {
    if (base_condition)
        return result;
    else
        return function_name(smaller_problem);
}

---

👨‍💻 1. Factorial Using Recursion

#include <stdio.h>

int factorial(int n) {
    if (n == 0 || n == 1)
        return 1;
    else
        return n * factorial(n - 1);
}

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    printf("Factorial of %d is %d\n", num, factorial(num));
    return 0;
}

---

👨‍💻 2. Fibonacci Series Using Recursion

#include <stdio.h>

int fibonacci(int n) {
    if (n == 0) return 0;
    if (n == 1) return 1;
    return fibonacci(n - 1) + fibonacci(n - 2);
}

int main() {
    int terms;
    printf("Enter number of terms: ");
    scanf("%d", &terms);
    printf("Fibonacci Series: ");
    for (int i = 0; i < terms; i++) {
        printf("%d ", fibonacci(i));
    }
    return 0;
}

⚠️ Note: Recursive Fibonacci is inefficient for large n – we’ll optimize it later with memoization or iteration.

---

👨‍💻 3. Sum of Array Using Recursion

#include <stdio.h>

int sumArray(int arr[], int n) {
    if (n == 0) return 0;
    return arr[n - 1] + sumArray(arr, n - 1);
}

int main() {
    int arr[100], n;
    printf("Enter number of elements: ");
    scanf("%d", &n);
    printf("Enter %d elements:\n", n);
    for (int i = 0; i < n; i++)
        scanf("%d", &arr[i]);

    printf("Sum of array = %d\n", sumArray(arr, n));
    return 0;
}

---

🧪 Practice Problems:

1. Find the GCD of two numbers using recursion.

2. Write a recursive function to calculate the power (xⁿ).

3. Reverse an array using recursion.

---

📘 Homework for Day 4:

• Compare iteration vs recursion by writing factorial using loops.

• Try writing Fibonacci with memoization or using a loop.

• LeetCode problem suggestion: Climbing Stairs – this is basically Fibonacci!

---

📅 Day 4 Summary:

• ✅ Understood recursion

• ✅ Implemented factorial, Fibonacci, and sum via recursion

• ✅ Practiced recursive thinking

🚀 DSA with C – Day 3: Bubble Sort & Binary Search

 

🎯 Goal:

• Learn Bubble Sort and sort arrays.

• Understand how Binary Search works.

• Compare Linear vs Binary Search.

• Practice problems on sorted arrays.

---

🧠 Theory

✅ Bubble Sort:

• Repeatedly compares adjacent elements and swaps them if they’re in the wrong order.

• Worst-case time complexity: O(n²)

• Best-case (already sorted): O(n) with optimization

---

👨‍💻 Bubble Sort in C

#include <stdio.h>

int main() {
    int arr[100], n, i, j, temp;

    printf("Enter number of elements: ");
    scanf("%d", &n);
    printf("Enter %d elements:\n", n);
    for (i = 0; i < n; i++)
        scanf("%d", &arr[i]);

    // Bubble Sort
    for (i = 0; i < n - 1; i++) {
        int swapped = 0;
        for (j = 0; j < n - i - 1; j++) {
            if (arr[j] > arr[j + 1]) {
                // Swap
                temp = arr[j];
                arr[j] = arr[j + 1];
                arr[j + 1] = temp;
                swapped = 1;
            }
        }
        if (swapped == 0)
            break; // Already sorted
    }

    printf("Sorted array:\n");
    for (i = 0; i < n; i++)
        printf("%d ", arr[i]);

    return 0;
}

---

✅ Binary Search:

• Efficient searching technique on sorted arrays.

• Time Complexity: O(log n)

• Repeatedly divide the array and compare with middle element.

---

👨‍💻 Binary Search in C

#include <stdio.h>

int binarySearch(int arr[], int n, int key) {
    int low = 0, high = n - 1, mid;

    while (low <= high) {
        mid = (low + high) / 2;

        if (arr[mid] == key)
            return mid;
        else if (arr[mid] < key)
            low = mid + 1;
        else
            high = mid - 1;
    }

    return -1; // Not found
}

int main() {
    int arr[100], n, key;

    printf("Enter number of elements: ");
    scanf("%d", &n);
    printf("Enter %d sorted elements:\n", n);
    for (int i = 0; i < n; i++)
        scanf("%d", &arr[i]);

    printf("Enter element to search: ");
    scanf("%d", &key);

    int result = binarySearch(arr, n, key);
    if (result == -1)
        printf("Element not found.\n");
    else
        printf("Element found at index %d.\n", result);

    return 0;
}

---

🔁 Linear vs Binary Search

Feature	Linear Search	Binary Search
Time Complexity	O(n)	O(log n)
Sorted Array Required	❌ No	✅ Yes
Speed	Slower	Faster for large data
Approach	Scan all elements	Divide & Conquer

🧪 Practice Problems:

1. Sort an array using Bubble Sort in descending order.

2. Count how many swaps were done during Bubble Sort.

3. Use Binary Search to find the number of occurrences of a given element.

4. If not found in Binary Search, return where it should be inserted.

---

📘 Homework for Day 3:

• Implement recursive Binary Search.

• Write a program that first sorts using Bubble Sort and then searches using Binary Search.

• LeetCode problem suggestion: Search Insert Position

---

📅 Day 3 Summary

• ✅ Learned Bubble Sort (with optimization)

• ✅ Implemented Binary Search (iterative)

• ✅ Practiced comparing search algorithms