NEB Class 12 Computer Science: Unit 4 - Programming in C [9 Marks]

Table of Contents

• 1. Review of C Fundamentals & Functions
• 2. Function Accessing (Call by Value)
• 3. Concept of Storage: Automatic & External
• 4. Concept of Recursion
• 5. Pointers in C
• 6. Structure and Union
• 7. Practice Questions & Board Exam Solutions

1. Review of C Fundamentals & Functions

C is a structured, procedure-oriented programming language created by Dennis Ritchie. Functions are self-contained code blocks designed to complete a specific task, promoting modular programming.

Types of Functions

• Library Functions: Pre-written functions included with C header files (e.g., printf(), scanf(), sqrt()).
• User-Defined Functions: Custom functions created by programmers to solve specific sub-problems.

Function Essentials

1. Prototype (Declaration): Informs the compiler about the function's name, parameters, and return type before it runs.
   int multiply(int, int);
2. Definition: Contains the core code block executed during execution.
3. Call: Executes the function from main() or another function.
4. Return Statement: Passes a value back to the caller function.

2. Accessing a Function by Passing Values (Call by Value)

In Call by Value, a duplicate copy of the argument's data is sent to the function parameters. Modifying variables inside the function body does not affect the original variables in main().

#include <stdio.h>

// Function Prototype
void updateMarks(int score);

int main() {
    int studentScore = 75;
    printf("Original Score before call = %d\n", studentScore);
    
    updateMarks(studentScore); // Call by Value
    
    printf("Original Score after call = %d\n", studentScore); // Value stays 75
    return 0;
}

void updateMarks(int score) {
    score = score + 10; // Changes local copy only
    printf("Updated Score inside function = %d\n", score);
}

3. Concept of Storage: Automatic & External

Storage classes determine where variables are saved, their default starting values, scope, and lifespan.

4. Concept of Recursion

Recursion is a programming approach where a function calls itself repeatedly until it satisfies a base terminating condition.

A. Factorial Program using Recursion

#include <stdio.h>

long int findFactorial(int n) {
    if (n <= 1) {
        return 1; // Base Case
    }
    return n * findFactorial(n - 1); // Recursive Step
}

int main() {
    int number = 6;
    printf("Factorial of %d = %ld\n", number, findFactorial(number));
    return 0;
}

B. Fibonacci Series Program using Recursion

#include <stdio.h>

int getFibonacci(int term) {
    if (term == 0) return 0; // Base Case 1
    if (term == 1) return 1; // Base Case 2
    return getFibonacci(term - 1) + getFibonacci(term - 2); // Recursive Step
}

int main() {
    int totalTerms = 6, i;
    printf("Fibonacci Series: ");
    for (i = 0; i < totalTerms; i++) {
        printf("%d ", getFibonacci(i));
    }
    printf("\n");
    return 0;
}

5. Pointers in C

A pointer is a variable designed to hold the memory address location of another variable.

#include <stdio.h>

int main() {
    int val = 50;
    int *ptr = &val; // Assign address of val to pointer

    printf("Value of val: %d\n", val);
    printf("Memory Address of val (&val): %p\n", ptr);
    printf("Value accessed via Dereferenced Pointer (*ptr): %d\n", *ptr);

    *ptr = 100; // Altering value directly via memory address
    printf("New value of val after dereference update: %d\n", val);
    return 0;
}

6. Structure and Union

Comparison: Structure vs. Union

Structure & Array of Structures Example

#include <stdio.h>

struct Book {
    char title[40];
    int pages;
    float price;
};

int main() {
    struct Book library[2]; // Array of structures for 2 books

    for (int i = 0; i < 2; i++) {
        printf("Enter title, pages, and price for Book %d:\n", i + 1);
        scanf("%s %d %f", library[i].title, &library[i].pages, &library[i].price);
    }

    printf("\n--- Book Catalog ---\n");
    for (int i = 0; i < 2; i++) {
        printf("Book %d: %s | Pages: %d | Price: Rs. %.2f\n", 
                i + 1, library[i].title, library[i].pages, library[i].price);
    }
    return 0;
}

7. Practice Questions & Board Exam Solutions

Short Practice Questions

1. Differentiate between library functions and user-defined functions.
   Answer: Library functions are built-in functions provided by C compilers (e.g., printf(), sqrt()) accessed via header files. User-defined functions are written by programmers to perform custom routines within an application.
2. What is the function of a return statement?
   Answer: A return statement immediately terminates function execution and sends a calculated value back to the calling function.
3. Explain Call by Value briefly.
   Answer: It copies argument data values into function parameters. Changes inside the function do not alter the source variables in the calling routine.
4. What is a pointer in C?
   Answer: A pointer is a variable that stores a memory address location of another variable. Declared using int *ptr; for integer types.

Sample NEB Board Exam Long Questions (8 Marks)

Question 1: Write a C program to generate the Fibonacci series up to 'n' terms using a recursive function. Explain recursion with its pros and cons.

#include <stdio.h>

// Recursive function declaration
int fibonacciTerm(int n) {
    if (n == 0) return 0; // Base Case 1
    if (n == 1) return 1; // Base Case 2
    return fibonacciTerm(n - 1) + fibonacciTerm(n - 2); // Recursive Step
}

int main() {
    int total, i;
    printf("Enter number of terms for Fibonacci series: ");
    scanf("%d", &total);

    if (total <= 0) {
        printf("Please enter a positive integer.\n");
    } else {
        printf("Fibonacci Sequence: ");
        for (i = 0; i < total; i++) {
            printf("%d ", fibonacciTerm(i));
        }
        printf("\n");
    }
    return 0;
}

Question 2: Define Structure and Union in C. Explain their core differences with programmatic examples.

#include <stdio.h>

// Structure Example
struct StudentRecord {
    int id;
    float gpa;
};

// Union Example
union StudentData {
    int id;
    float gpa;
};

int main() {
    struct StudentRecord s = {101, 3.8};
    union StudentData u;

    printf("--- STRUCTURE (Separate Memory Allocation) ---\n");
    printf("ID: %d | GPA: %.2f\n", s.id, s.gpa);
    printf("Size of Structure: %lu bytes\n\n", sizeof(struct StudentRecord));

    printf("--- UNION (Shared Memory Allocation) ---\n");
    u.id = 202;
    printf("ID assigned: %d\n", u.id);
    
    u.gpa = 3.9; // Overwrites ID memory
    printf("GPA assigned: %.2f\n", u.gpa);
    printf("ID value after GPA update (corrupted): %d\n", u.id);
    printf("Size of Union: %lu bytes\n", sizeof(union StudentData));

    return 0;
}