Writing first C program - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to include the standard input-output header.

C

#include [1]

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

A<stdlib.h>

B<math.h>

C<stdio.h>

D<string.h>

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong header that doesn't provide printf.

Forgetting the angle brackets around the header name.

The <stdio.h> header is needed for input and output functions like printf.

2fill in blank

medium

Complete the code to start the main function.

C

int [1]() {

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

Astart

Brun

Cbegin

Dmain

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different function name instead of main.

Omitting the parentheses after the function name.

The main function is the entry point of a C program.

3fill in blank

hard

Fix the error in the printf statement to print Hello World.

C

printf([1]);

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

A"Hello World"

B'Hello World'

CHello World

DHello World;

Attempts:

3 left

💡 Hint

Common Mistakes

Using single quotes which are for single characters.

Not using any quotes causing a syntax error.

The string to print must be inside double quotes "" in C.

4fill in blank

hard

Fill the blank to correctly end the main function with a return statement.

C

    return [1];
}

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

A1

B0

Cmain

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Returning 1 which usually means an error.

Returning the function name or void which is invalid.

Returning 0 from main means the program ended successfully.

5fill in blank

hard

Fill all three blanks to complete the full Hello World program.

C

#include [1]

int [2]() {
    printf([3]);
    return 0;
}

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

A<stdio.h>

Bmain

C"Hello World"

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Missing the header include.

Wrong function name or missing parentheses.

Not quoting the string in printf.

This is the complete minimal C program that prints Hello World.

Practice

1. What is the purpose of the int main() function in a C program?

easy

A. It prints messages to the screen.

B. It is the starting point where the program begins execution.

C. It declares variables for the program.

D. It ends the program immediately.

Solution

1. Step 1: Understand the role of main()

   The main() function is where the program starts running in C.

2. Step 2: Identify the correct purpose

   It is not for declaring variables or printing messages but for starting the program.

3. Final Answer:

   It is the starting point where the program begins execution. -> Option B

4. Quick Check:

   Program starts at main() [OK]

Hint: Remember: C programs always start at main() [OK]

Common Mistakes:

• Thinking main() prints output
• Confusing main() with variable declaration
• Believing main() ends the program immediately

2. Which of the following is the correct syntax to print "Hello, World!" in C?

easy

A. printf("Hello, World!");

B. printf("Hello, World!")

C. print("Hello, World!");

D. echo("Hello, World!");

Solution

1. Step 1: Identify the correct function for output

   In C, printf is used to print text to the screen.

2. Step 2: Check syntax details

   Each statement must end with a semicolon ;. So printf("Hello, World!"); is correct.

3. Final Answer:

   printf("Hello, World!"); -> Option A

4. Quick Check:

   Use printf with semicolon [OK]

Hint: Always end printf with a semicolon [OK]

Common Mistakes:

• Missing semicolon at the end
• Using print instead of printf
• Using echo which is not C syntax

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

#include 
int main() {
    printf("Welcome to C programming!\n");
    return 0;
}

medium

A. No output

B. Welcome to C programming!\n

C. Syntax Error

D. Welcome to C programming!

Solution

1. Step 1: Understand the printf statement

   The string inside printf includes \n which means new line after printing.

2. Step 2: Predict the output

   The program prints "Welcome to C programming!" followed by a new line.

3. Final Answer:

   Welcome to C programming! -> Option D

4. Quick Check:

   \n creates new line, output is plain text [OK]

Hint: \n means new line, not literal text [OK]

Common Mistakes:

• Thinking \n prints as text
• Expecting syntax error due to \n
• Ignoring the return statement effect

4. Identify the error in the following C program:

#include 
int main() {
    printf("Hello World")
    return 0;
}

medium

A. Incorrect header file included

B. Missing return type for main

C. Missing semicolon after printf statement

D. Missing main function

Solution

1. Step 1: Check each statement for syntax

   The printf statement is missing a semicolon at the end.

2. Step 2: Verify other parts

   The main function has correct return type and header file is correct.

3. Final Answer:

   Missing semicolon after printf statement -> Option C

4. Quick Check:

   Every statement ends with ; [OK]

Hint: Look for missing semicolons after statements [OK]

Common Mistakes:

• Ignoring missing semicolon errors
• Thinking return type is missing
• Assuming wrong header file causes error

5. You want to write a C program that prints two lines: "Hello!" and "Welcome to C." Which code snippet correctly does this?

hard

A. #include
int main() {
printf("Hello!\n");
printf("Welcome to C.\n");
return 0;
}

B. #include
int main() {
printf("Hello!Welcome to C.\n");
return 0;
}

C. #include
int main() {
printf("Hello!");
printf("Welcome to C.\n");
return 0;
}

D. #include
int main() {
printf("Hello!");
printf("Welcome to C.");
return 0;
}

Solution

1. Step 1: Understand how to print two lines

   Each line should end with a newline character \n to move to the next line.

2. Step 2: Check each option for correct newlines

   #include int main() { printf("Hello!\n"); printf("Welcome to C.\n"); return 0; } prints "Hello!" with \n and "Welcome to C." with \n, so two lines appear.

3. Final Answer:

   Two printf statements, each ending with \n -> Option A

4. Quick Check:

   Use \n at end of each line for separate lines [OK]

Hint: Use \n after each line to print on new lines [OK]

Common Mistakes:

• Missing \n causing lines to join
• Putting \n only on first line
• Not returning 0 at end of main