Reusability and maintenance - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Modular Function Calls

What is the output of this C program that uses a reusable function to calculate the square of a number?

C

#include <stdio.h>

int square(int x) {
    return x * x;
}

int main() {
    int a = 3, b = 4;
    printf("%d %d\n", square(a), square(b));
    return 0;
}

A 9 16

B 3 4

C 6 8

D 12 16

💡 Hint

Remember the function returns the square of the input.

The function square multiplies the input by itself. So square(3) is 9 and square(4) is 16.

❓ Predict Output

intermediate

Output of Code Using Header File Inclusion

Given the following files, what will be the output when compiled and run?

math_ops.h
int add(int x, int y);

math_ops.c
int add(int x, int y) { return x + y; }

main.c
#include
#include "math_ops.h"
int main() {
printf("%d\n", add(5, 7));
return 0;
}

A Runtime error

B 57

C 12

D Compiler error due to missing function definition

💡 Hint

Check if the function is properly declared and defined.

The function add is declared in the header and defined in math_ops.c. When linked properly, it returns 5 + 7 = 12.

🔧 Debug

advanced

Identify the Cause of Unexpected Output

What causes the unexpected output in this C program that tries to reuse a function to increment a value?

#include <stdio.h>

void increment(int x) {
    x = x + 1;
}

int main() {
    int a = 5;
    increment(a);
    printf("%d\n", a);
    return 0;
}

A The printf statement has wrong format specifier

B The function is missing a return statement

C The variable 'a' is not initialized

D The function increments a copy of the variable, not the original

💡 Hint

Think about how arguments are passed to functions in C.

In C, function arguments are passed by value, so increment changes only a copy of a. The original a remains unchanged.

📝 Syntax

advanced

Identify the Syntax Error in Modular Code

Which option contains the syntax error that prevents this modular C code from compiling?

#include <stdio.h>

int multiply(int x, int y) {
    return x * y
}

int main() {
    printf("%d\n", multiply(3, 4));
    return 0;
}

A Missing semicolon after return statement in multiply function

B Missing return type for multiply function

C Missing parentheses in printf call

D Missing main function return statement

💡 Hint

Check punctuation carefully in function bodies.

The return statement in multiply lacks a semicolon, causing a syntax error.

🚀 Application

expert

Number of Functions in a Modular Program

Consider a C program split into three files: main.c, utils.c, and math.c. utils.c has 4 functions, math.c has 3 functions, and main.c has 2 functions. How many functions are available for reuse across the entire program after linking?

A 3

B 9

C 7

D 2

💡 Hint

Count all functions defined in all files.

All 4 + 3 + 2 functions are compiled and linked, so 9 functions are available for reuse.

Practice

1. What is the main benefit of using functions in C for reusability and maintenance?

easy

A. Functions use less memory than variables

B. Functions make the program run faster

C. You can write code once and use it many times

D. Functions prevent all bugs automatically

Solution

1. Step 1: Understand the purpose of functions

   Functions allow you to group code that performs a task so you can reuse it multiple times without rewriting.

2. Step 2: Connect reusability to maintenance

   Using functions reduces repeated code, making it easier to update and maintain.

3. Final Answer:

   You can write code once and use it many times -> Option C

4. Quick Check:

   Functions improve reusability = You can write code once and use it many times [OK]

Hint: Functions let you reuse code easily [OK]

Common Mistakes:

• Thinking functions always make code faster
• Confusing functions with variables
• Believing functions fix all bugs automatically

2. Which of the following is the correct syntax to declare a function named add that takes two integers and returns an integer in C?

easy

A. int add(int a, int b);

B. add int(int a, int b);

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

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

Solution

1. Step 1: Identify correct function declaration syntax

   In C, a function declaration specifies the return type, function name, and parameter types inside parentheses.

2. Step 2: Check each option

   int add(int a, int b); matches the correct syntax: int add(int a, int b);. Others have wrong order, keywords, or syntax.

3. Final Answer:

   int add(int a, int b); -> Option A

4. Quick Check:

   Correct C function declaration = int add(int a, int b); [OK]

Hint: Function declarations start with return type and name [OK]

Common Mistakes:

• Using 'function' keyword (not in C)
• Wrong parameter syntax
• Missing return type

3. What will be the output of the following C code?

int square(int x) {
    return x * x;
}

int main() {
    int result = square(4);
    printf("%d", result);
    return 0;
}

medium

A. Compilation error

B. 8

C. 4

D. 16

Solution

1. Step 1: Understand the function behavior

   The function square returns the input multiplied by itself, so square(4) returns 16.

2. Step 2: Check the main function output

   The main function calls square(4), stores 16 in result, and prints it with printf.

3. Final Answer:

   16 -> Option D

4. Quick Check:

   square(4) = 16 [OK]

Hint: Multiply input by itself to find square [OK]

Common Mistakes:

• Confusing multiplication with addition
• Expecting 8 instead of 16
• Thinking code has syntax errors

4. Identify the error in the following C code that tries to reuse a function:

int multiply(int a, int b) {
    return a * b;
}

int main() {
    int result = multiply(5);
    printf("%d", result);
    return 0;
}

medium

A. multiply is called with only one argument instead of two

B. main function should return void

C. printf format specifier is incorrect

D. Function multiply is missing a return statement

Solution

1. Step 1: Check function definition and call

   The function multiply requires two integer arguments, but in main it is called with only one argument.

2. Step 2: Identify the error type

   This mismatch causes a compilation error because the number of arguments does not match the function signature.

3. Final Answer:

   multiply is called with only one argument instead of two -> Option A

4. Quick Check:

   Argument count mismatch = multiply is called with only one argument instead of two [OK]

Hint: Match function call arguments to definition [OK]

Common Mistakes:

• Ignoring argument count mismatch
• Thinking printf format is wrong
• Assuming main must return void

5. You want to write a reusable function in C that calculates the average of an array of integers. Which approach improves reusability and maintenance the most?

hard

A. Write the average calculation code inside main() every time you need it

B. Create a function that takes an integer array and its size, then returns the average

C. Use global variables to store the array and size, then write a function without parameters

D. Copy and paste the average calculation code wherever needed

Solution

1. Step 1: Understand reusability principles

   Reusable code should be modular, accept inputs, and avoid global state to be flexible and maintainable.

2. Step 2: Evaluate each option

   Create a function that takes an integer array and its size, then returns the average creates a function with parameters for array and size, making it reusable for any array. Others either duplicate code or rely on globals, reducing reusability.

3. Final Answer:

   Create a function that takes an integer array and its size, then returns the average -> Option B

4. Quick Check:

   Function with parameters improves reusability = Create a function that takes an integer array and its size, then returns the average [OK]

Hint: Functions with parameters are reusable and maintainable [OK]

Common Mistakes:

• Using global variables reduces flexibility
• Duplicating code increases errors
• Writing code only inside main limits reuse