Function declaration and definition - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a function named add that takes two integers and returns an integer.

C

int [1](int a, int b);

Drag options to blanks, or click blank then click option'

Aadd

Bsum

Ctotal

Dcalculate

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different function name than add.

Forgetting the semicolon at the end of the declaration.

The function declaration uses the function name add as specified.

2fill in blank

medium

Complete the code to define the function add that returns the sum of two integers.

C

int add(int a, int b) {
    return a [1] b;
}

Drag options to blanks, or click blank then click option'

A+

B/

C*

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

Forgetting the return statement.

The function returns the sum of a and b using the plus operator.

3fill in blank

hard

Fix the error in the function declaration to correctly declare a function named multiply that takes two integers and returns an integer.

C

int multiply(int a, int b)[1]

Drag options to blanks, or click blank then click option'

A[]

B{}

C()

D;

Attempts:

3 left

💡 Hint

Common Mistakes

Using curly braces instead of a semicolon for declarations.

Using parentheses or brackets incorrectly.

A function declaration ends with a semicolon ; to indicate it is only a declaration.

4fill in blank

hard

Fill both blanks to define a function named subtract that returns the difference of two integers.

C

int [1](int a, int b) {
    return a [2] b;
}

Drag options to blanks, or click blank then click option'

Asubtract

B+

C-

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using the plus operator instead of minus.

Using the wrong function name.

The function name is subtract and the operator for subtraction is -.

5fill in blank

hard

Fill all three blanks to define a function named max_of_two that returns the greater of two integers.

C

int [1](int a, int b) {
    if (a [2] b) {
        return [3];
    } else {
        return b;
    }
}

Drag options to blanks, or click blank then click option'

Amax_of_two

B<

Ca

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong comparison operator.

Returning the wrong variable in the if block.

The function name is max_of_two. The condition checks if a > b, then returns a if true, else returns b.

Practice

1. What is the purpose of a function declaration in C?

easy

A. To allocate memory for variables inside the function

B. To execute the function's code

C. To tell the compiler about the function's name, return type, and parameters before its use

D. To print the function's output

Solution

1. Step 1: Understand function declaration role

   A function declaration informs the compiler about the function's name, return type, and parameters so it can be used before its definition.

2. Step 2: Differentiate declaration from definition

   Declaration does not contain the function's code; that is done in the definition.

3. Final Answer:

   To tell the compiler about the function's name, return type, and parameters before its use -> Option C

4. Quick Check:

   Function declaration = Inform compiler [OK]

Hint: Declaration tells compiler about function before use [OK]

Common Mistakes:

• Confusing declaration with definition
• Thinking declaration runs the function
• Assuming declaration allocates memory

2. Which of the following is a correct function declaration in C?

easy

A. int add { int a, int b; };

B. int add(int a, int b) {}

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

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

Solution

1. Step 1: Identify correct syntax for declaration

   A function declaration includes the return type, function name, parameter list, and ends with a semicolon.

2. Step 2: Check each option

   int add(int a, int b); matches correct syntax: return type 'int', name 'add', parameters '(int a, int b)', and semicolon. Others have syntax errors or missing semicolon.

3. Final Answer:

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

4. Quick Check:

   Declaration ends with semicolon [OK]

Hint: Declaration ends with semicolon and no body [OK]

Common Mistakes:

• Missing semicolon at end
• Including function body in declaration
• Wrong parameter syntax

3. What will be the output of this C program?

#include <stdio.h>

int multiply(int x, int y);

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

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

medium

A. 12

B. 7

C. 34

D. Compilation error

Solution

1. Step 1: Understand function declaration and call

   The function 'multiply' is declared before main and defined after. main calls multiply(3, 4).

2. Step 2: Calculate function return value

   multiply returns 3 * 4 = 12, which is printed by printf.

3. Final Answer:

   12 -> Option A

4. Quick Check:

   3 * 4 = 12 [OK]

Hint: Declaration allows call before definition [OK]

Common Mistakes:

• Thinking declaration runs code
• Confusing output with parameters
• Expecting compilation error due to declaration

4. Identify the error in this function declaration and definition:

int sum(int a, int b)
{
    return a + b
}

medium

A. Function name is invalid

B. Missing semicolon after return statement

C. Parameters must be declared outside parentheses

D. Return type should be void

Solution

1. Step 1: Check syntax inside function body

   The return statement must end with a semicolon in C.

2. Step 2: Identify missing semicolon

   Here, 'return a + b' lacks a semicolon, causing a syntax error.

3. Final Answer:

   Missing semicolon after return statement -> Option B

4. Quick Check:

   Statements end with semicolon [OK]

Hint: Return statements need semicolon [OK]

Common Mistakes:

• Omitting semicolon after return
• Misunderstanding parameter syntax
• Changing return type unnecessarily

5. You want to declare and define a function that calculates the average of three integers and returns a float. Which of the following is the correct declaration and definition?

hard

A. float average(int a, int b, int c);

float average(int a, int b, int c) {
return (a + b + c) / 3.0;
}

B. int average(int a, int b, int c);

int average(int a, int b, int c) {
return (a + b + c) / 3.0;
}

C. float average(int a, int b, int c);

float average(int a, int b, int c) {
return (a + b + c) / 3;
}

D. float average(int a, int b, int c) {
return (a + b + c) / 3;
}

Solution

1. Step 1: Check function declaration matches definition

   Declaration and definition must have same return type (float) and parameters (three ints).

2. Step 2: Ensure correct calculation for float average

   To get float result, divide by 3.0 (float), not 3 (int).

3. Step 3: Verify other options

   Integer division (/ 3) causes truncation. Declaring int return but dividing by 3.0 causes type mismatch. Missing declaration prevents prior use.

4. Final Answer:

   float average(int a, int b, int c); float average(int a, int b, int c) { return (a + b + c) / 3.0; } -> Option A

5. Quick Check:

   Float division needs 3.0 [OK]

Hint: Use float division (3.0) and matching declaration [OK]

Common Mistakes:

• Using integer division instead of float
• Mismatching declaration and definition types
• Omitting function declaration