Assignment 3: Function Library | C Programming Course

Assignment Overview

Functions are the building blocks of modular programming in C. In this assignment, you will create a library of useful utility functions that can be reused across multiple programs. This comprehensive project requires you to apply ALL concepts from Module 3: function declarations, definitions, prototypes, parameter passing, return values, scope, storage classes, and recursion.

No Standard Library Shortcuts: For string utilities, you must NOT use <string.h> functions. Implement strlen, strcpy, strcmp, and strrev from scratch to demonstrate your understanding.

Skills Applied: This assignment tests your understanding of Functions (3.1), Storage Classes (3.2), and Scope and Lifetime (3.3) from Module 3.

Function Basics (3.1)

Declaration, definition, prototypes, calling conventions

Storage Classes (3.2)

auto, static, extern, register keywords

Scope and Lifetime (3.3)

Local, global, block scope, variable lifetime

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Tasks

Your function library must implement ALL of the following modules. Each file will be tested individually.

Math Utilities

Create math_utils.c with the following functions:

int max(int a, int b) - Returns the larger of two numbers
int min(int a, int b) - Returns the smaller of two numbers
int abs_val(int n) - Returns absolute value
double power(double base, int exp) - Returns base raised to exp
int gcd(int a, int b) - Returns greatest common divisor

// math_utils.c - Example structure
#include <stdio.h>

int max(int a, int b) {
    return (a > b) ? a : b;
}

int min(int a, int b) {
    // Your implementation
}

// ... more functions

int main() {
    // Test all functions
    printf("max(5, 3) = %d\n", max(5, 3));  // 5
    return 0;
}

Number Analysis

Create number_analysis.c with:

int is_prime(int n) - Returns 1 if prime, 0 otherwise
int is_even(int n) - Returns 1 if even, 0 if odd
int digit_count(int n) - Returns number of digits
int sum_of_digits(int n) - Returns sum of all digits
int reverse_number(int n) - Returns reversed number

// number_analysis.c - Example
int is_prime(int n) {
    if (n <= 1) return 0;
    for (int i = 2; i * i <= n; i++) {
        if (n % i == 0) return 0;
    }
    return 1;
}

int main() {
    printf("is_prime(17) = %d\n", is_prime(17));  // 1
    printf("is_prime(4) = %d\n", is_prime(4));    // 0
    return 0;
}

Recursive Functions

Create recursive.c with:

int factorial(int n) - Recursive factorial calculation
int fibonacci(int n) - Recursive nth Fibonacci number
int sum_to_n(int n) - Recursive sum from 1 to n
void print_binary(int n) - Print number in binary recursively

Important: Each function MUST use recursion, not iteration! You will receive zero points for iterative solutions.

// recursive.c - Example
int factorial(int n) {
    if (n <= 1) return 1;       // Base case
    return n * factorial(n - 1); // Recursive case
}

void print_binary(int n) {
    if (n > 1) print_binary(n / 2);
    printf("%d", n % 2);
}

String Utilities (without string.h)

Create string_utils.c with custom implementations:

int str_length(char str[]) - Returns string length
void str_reverse(char str[]) - Reverses string in place
int str_compare(char s1[], char s2[]) - Compares two strings
void str_copy(char dest[], char src[]) - Copies source to destination

Restriction: Do NOT use <string.h> - implement all string operations from scratch!

// string_utils.c - Example
int str_length(char str[]) {
    int len = 0;
    while (str[len] != '\0') {
        len++;
    }
    return len;
}

int main() {
    printf("Length: %d\n", str_length("hello"));  // 5
    return 0;
}

Main Driver Program

Create main.c that:

Demonstrates all functions from all utility files
Implements a menu system for user to test different utilities
Handles user input validation gracefully
Uses proper function prototypes in a header file or at top of main.c

// main.c - Menu system example
#include <stdio.h>

// Function prototypes
int max(int a, int b);
int is_prime(int n);
int factorial(int n);
int str_length(char str[]);

int main() {
    int choice;
    
    printf("=== Function Library ===\n");
    printf("1. Math Utilities\n");
    printf("2. Number Analysis\n");
    printf("3. Recursive Functions\n");
    printf("4. String Utilities\n");
    printf("5. Exit\n");
    printf("Choice: ");
    scanf("%d", &choice);
    
    // Handle menu selection...
    return 0;
}

Submission

Create a public GitHub repository with the exact name shown below:

Required Repository Name

c-function-library

github.com/<your-username>/c-function-library

Required Files

c-function-library/
├── math_utils.c        # 5 math utility functions
├── number_analysis.c   # 5 number analysis functions
├── recursive.c         # 4 recursive functions
├── string_utils.c      # 4 string utility functions
├── main.c              # Driver program with menu system
└── README.md           # REQUIRED - see contents below

README.md Must Include:

Your full name and submission date
Brief description of each utility file and its functions
Compilation instructions (gcc commands)
Any challenges faced and how you solved them

Do Include

All 18+ functions implemented and working
Comments explaining complex logic
Test cases in main() for each function
Proper function prototypes
Clean, indented, readable code
README.md with all required sections

Do Not Include

Compiled binaries (.exe, .out files)
Object files (.o files)
IDE-specific folders (.vscode, .idea)
Code that does not compile without errors
Iterative solutions for recursive tasks
string.h usage in string_utils.c

Important: Before submitting, compile and test all your code to ensure it runs without errors. Use: gcc -o main main.c math_utils.c number_analysis.c recursive.c string_utils.c

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Grading Rubric

Your assignment will be graded on the following criteria:

Criteria	Points	Description
Math Utilities	20	All 5 functions work correctly with various inputs
Number Analysis	20	All 5 functions work correctly, including edge cases
Recursive Functions	25	Proper recursion used (not iteration), correct base cases
String Utilities	20	Custom implementations without string.h, handles edge cases
Main Driver	15	Menu system works, proper testing, input validation
Total	100

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What You Will Practice

Function Design (3.1)

Writing modular functions with proper declarations, definitions, prototypes, parameters, and return values

Storage Classes (3.2)

Understanding auto, static, extern, and register keywords for controlling variable storage and visibility

Scope and Lifetime (3.3)

Managing local vs global variables, block scope, and understanding when variables are created and destroyed

Recursive Thinking

Breaking problems into base cases and recursive cases, understanding call stack behavior

Pro Tips

C Best Practices

Use meaningful function and variable names
Always declare function prototypes
Handle edge cases (negative numbers, zero, empty strings)
Test functions with multiple inputs

Recursion Tips

Always define a clear base case first
Ensure recursive calls move toward base case
Trace through small examples on paper
Watch for stack overflow with large inputs

Time Management

Start with the simplest functions first
Build and test incrementally
Leave time for the menu driver program
Test compilation frequently

Common Mistakes

Forgetting to handle negative numbers in digit functions
Using loops instead of recursion
Missing null terminator in string operations
Integer overflow in factorial for large n

Function Library

What You'll Practice

Contents

Assignment Overview

Function Basics (3.1)

Storage Classes (3.2)

Scope and Lifetime (3.3)

Tasks

Math Utilities

Number Analysis

Recursive Functions

String Utilities (without string.h)

Main Driver Program

Submission

Required Repository Name

Required Files

README.md Must Include:

Do Include

Do Not Include

Grading Rubric

Ready to Submit?

What You Will Practice

Function Design (3.1)

Storage Classes (3.2)

Scope and Lifetime (3.3)

Recursive Thinking

Pro Tips

C Best Practices

Recursion Tips

Time Management

Common Mistakes

Pre-Submission Checklist

Code Requirements

Repository Requirements