Function parameters

Introduction

Function parameters let you send information into a function so it can use that information to do its job.

When you want a function to work with different values each time you call it.

When you want to reuse the same function for many tasks with different inputs.

When you want to organize your code by breaking it into smaller parts that need data.

When you want to make your program easier to read and maintain by avoiding repeated code.

Syntax

C

return_type function_name(type1 param1, type2 param2, ...) {
    // function body
}

Parameters are listed inside the parentheses after the function name.

Each parameter has a type and a name, separated by a space.

Examples

A function with one parameter of type char array (string).

C

void greet(char name[]) {
    printf("Hello, %s!\n", name);
}

A function with two integer parameters that returns their sum.

C

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

A function with one integer parameter that prints it.

C

void printNumber(int number) {
    printf("Number: %d\n", number);
}

Sample Program

This program defines a function add that takes two numbers and returns their sum. In main, it calls add with 5 and 7 and prints the result.

C

#include <stdio.h>

// Function that adds two numbers and returns the result
int add(int x, int y) {
    return x + y;
}

int main() {
    int result = add(5, 7);
    printf("The sum of 5 and 7 is %d\n", result);
    return 0;
}

Important Notes

Parameters act like placeholders for the values you give when calling the function.

The names of parameters are local to the function and can be different from argument names.

If you don't provide the right number or type of arguments when calling, the program may not work correctly.

Summary

Function parameters let you send data into functions to work with.

They are defined by type and name inside the parentheses after the function name.

Using parameters makes your functions flexible and reusable.

Practice

1. What is the purpose of function parameters in C?

easy

A. To send data into functions so they can use it

B. To declare variables inside the main function

C. To print output on the screen

D. To create loops inside functions

Solution

1. Step 1: Understand function parameters

   Function parameters allow you to pass information into a function so it can use that data.

2. Step 2: Identify the correct purpose

   Creating loops inside functions, declaring variables inside the main function, and printing output on the screen describe other tasks, not the role of parameters.

3. Final Answer:

   To send data into functions so they can use it -> Option A

4. Quick Check:

   Function parameters = send data into functions [OK]

Hint: Parameters pass data into functions for flexibility [OK]

Common Mistakes:

• Confusing parameters with variables declared inside main
• Thinking parameters print output
• Mixing parameters with loop control

2. Which of the following is the correct way to declare a function with two integer parameters in C?

easy

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

B. void add(int a, b);

C. void add(int a int b);

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

Solution

1. Step 1: Check parameter syntax

   Parameters must be separated by commas and each must have a type and name.

2. Step 2: Identify correct syntax

   void add(int a, int b); correctly uses commas and types. void add(int a; int b); uses semicolon instead of comma. void add(int a int b); misses comma. void add(int a, b); misses type for second parameter.

3. Final Answer:

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

4. Quick Check:

   Parameters need type and comma [OK]

Hint: Separate parameters with commas and specify type for each [OK]

Common Mistakes:

• Using semicolons instead of commas between parameters
• Omitting type for parameters
• Missing commas between parameters

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

void printSum(int x, int y) {
    printf("%d\n", x + y);
}

int main() {
    printSum(3, 4);
    return 0;
}

medium

A. 7

B. 34

C. 0

D. Compilation error

Solution

1. Step 1: Understand function call and parameters

   The function printSum receives 3 and 4 as parameters and adds them.

2. Step 2: Calculate the sum and output

   3 + 4 equals 7, so printf prints 7 followed by a newline.

3. Final Answer:

   7 -> Option A

4. Quick Check:

   3 + 4 = 7 [OK]

Hint: Sum parameters inside function to get output [OK]

Common Mistakes:

• Thinking parameters concatenate as strings
• Expecting zero output without return
• Assuming syntax error due to missing includes

4. Identify the error in this function declaration:

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

medium

A. Return statement is incorrect

B. Function must return void

C. Missing type for parameter b

D. Function name is invalid

Solution

1. Step 1: Check parameter declarations

   Each parameter must have a type. Here, 'b' lacks a type.

2. Step 2: Confirm other parts are correct

   Return type int and function name are valid. Return statement syntax is correct.

3. Final Answer:

   Missing type for parameter b -> Option C

4. Quick Check:

   Every parameter needs a type [OK]

Hint: Declare type for every parameter explicitly [OK]

Common Mistakes:

• Omitting type for second or later parameters
• Assuming return type must be void
• Misreading return statement as error

5. You want to write a function that swaps two integers using pointers. Which function parameter list is correct?

hard

A. void swap(int &a, int &b)

B. void swap(int *a, int *b)

C. void swap(int a, int b)

D. void swap(int a*, int b*)

Solution

1. Step 1: Understand swapping with pointers

   To swap values in C, you pass pointers to the variables so the function can modify original data.

2. Step 2: Identify correct pointer syntax

   void swap(int *a, int *b) correctly declares two pointer parameters. void swap(int a, int b) passes by value (won't swap original). void swap(int &a, int &b) uses C++ reference syntax (invalid in C). void swap(int a*, int b*) has incorrect pointer syntax.

3. Final Answer:

   void swap(int *a, int *b) -> Option B

4. Quick Check:

   Use pointers to modify original variables [OK]

Hint: Use int * for pointer parameters to modify originals [OK]

Common Mistakes:

• Passing parameters by value when pointers are needed
• Using C++ reference syntax in C
• Incorrect pointer declaration syntax