Structure of a 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<string.h>

B<stdlib.h>

C"myheader.h"

D<stdio.h>

Attempts:

3 left

💡 Hint

Common Mistakes

Using instead of for input-output functions.

Forgetting the angle brackets around the header name.

The #include <stdio.h> directive includes the standard input-output library needed for functions like printf.

2fill in blank

medium

Complete the code to define the main function that returns an integer.

C

[1] main() {
    return 0;
}

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

Avoid

Bint

Cfloat

Dchar

Attempts:

3 left

💡 Hint

Common Mistakes

Using void as the return type for main.

Using data types like float or char for main.

The main function should return an int to indicate the program's exit status.

3fill in blank

hard

Fix the error in the code by completing the statement to print "Hello, World!".

C

#include <stdio.h>

int main() {
    [1]("Hello, World!\n");
    return 0;
}

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

Aprintf

Bprintln

Cprint

Dcout

Attempts:

3 left

💡 Hint

Common Mistakes

Using print or println which are not valid in C.

Using cout which is from C++.

The correct function to print formatted output in C is printf.

4fill in blank

hard

Fill both blanks to declare a variable and assign it a value inside main.

C

int main() {
    [1] [2] = 10;
    return 0;
}

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

Aint

Bfloat

Cnumber

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using float when the value is an integer.

Using invalid variable names like number which is not declared.

To declare an integer variable named count, use int count = 10;.

5fill in blank

hard

Fill all three blanks to complete a simple C program that prints a variable's value.

C

#include <stdio.h>

[1] main() {
    [2] [3] = 5;
    printf("Value: %d\n", [3]);
    return 0;
}

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

Aint

Cnum

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in declaration and print statement.

Using void as return type for main.

The main function returns int. Declare an integer variable num and print it.

Practice

1. Which part of a C program is mandatory to start the execution of the program?

easy

A. The return statement

B. The printf() statement

C. The #include directive

D. The main() function

Solution

1. Step 1: Understand program entry point

   In C, the program always starts executing from the main() function.

2. Step 2: Identify mandatory part for execution

   Without main(), the program has no defined starting point.

3. Final Answer:

   The main() function -> Option D

4. Quick Check:

   Program starts at main() [OK]

Hint: Look for the function where execution begins [OK]

Common Mistakes:

• Thinking printf() starts the program
• Confusing #include with execution start
• Assuming return starts the program

2. Which of the following is the correct way to include the standard input-output header in a C program?

easy

A. #include "stdio.h"

B. #include

C. include

D. #include stdio.h

Solution

1. Step 1: Recognize correct syntax for header inclusion

   The standard way to include system headers is using angle brackets: #include <header>.

2. Step 2: Check each option

   #include uses correct syntax: #include <stdio.h>. #include "stdio.h" uses quotes which is for user headers. Options C and D miss the # or angle brackets.

3. Final Answer:

   #include <stdio.h> -> Option B

4. Quick Check:

   System headers use <> brackets [OK]

Hint: Use #include with angle brackets for standard headers [OK]

Common Mistakes:

• Using quotes instead of angle brackets for standard headers
• Omitting the # symbol
• Missing angle brackets or quotes

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

#include <stdio.h>

int main() {
    printf("Hello, World!\n");
    return 0;
}

medium

A. Hello World

B. hello, world!

C. Hello, World!

D. Syntax Error

Solution

1. Step 1: Analyze the printf statement

   The program prints exactly the string inside quotes: "Hello, World!\n" which means it prints Hello, World! followed by a new line.

2. Step 2: Check for case and punctuation

   The output matches Hello, World! exactly, including capitalization and punctuation.

3. Final Answer:

   Hello, World! -> Option C

4. Quick Check:

   Output matches printf string exactly [OK]

Hint: Match output exactly with printf string [OK]

Common Mistakes:

• Ignoring case sensitivity
• Missing punctuation or newline
• Assuming syntax error without checking code

4. Identify the error in the following C program:

#include <stdio.h>

int main() {
    printf("Welcome to C programming!");
}

medium

A. Missing return statement in main function

B. Missing semicolon after printf statement

C. Incorrect header file included

D. No error, program is correct

Solution

1. Step 1: Check syntax of printf statement

   The printf line ends with a semicolon, so no syntax error there.

2. Step 2: Check main function return

   The main function is declared to return int but lacks a return statement, which can cause a warning or error depending on compiler settings.

3. Final Answer:

   Missing return statement in main function -> Option A

4. Quick Check:

   main() must return int value [OK]

Hint: Always include return 0; in main() [OK]

Common Mistakes:

• Assuming missing semicolon error
• Ignoring missing return in main
• Thinking header file is wrong

5. You want to write a C program that prints numbers from 1 to 5 using a loop inside the main() function. Which of the following code snippets correctly shows the structure of such a program?

hard

A. #include

int main() {
int i;
for(i = 1; i <= 5; i++) {
printf("%d\n", i);
}
return 0;
}

B. #include

void main() {
int i;
for(i = 1; i < 5; i++) {
printf("%d\n", i);
}
}

C. #include

int main() {
int i = 1;
while(i < 5) {
printf("%d\n", i);
i++;
}
return 0;
}

D. #include

int main() {
int i;
for(i = 1; i <= 5; i++)
printf("%d\n", i);
}

Solution

1. Step 1: Check loop range and printing

   #include int main() { int i; for(i = 1; i <= 5; i++) { printf("%d\n", i); } return 0; } uses a for loop from 1 to 5 inclusive, printing each number with newline, which matches the requirement.

2. Step 2: Verify program structure and correctness

   #include int main() { int i; for(i = 1; i <= 5; i++) { printf("%d\n", i); } return 0; } has correct int main(), includes return 0;, and proper syntax. Other options have issues: B uses void main() (not standard), loop range is incorrect; C loops only to 4; D misses braces which is allowed but less clear.

3. Final Answer:

   Option A is the correct and complete program structure -> Option A

4. Quick Check:

   Correct loop and main() structure [OK]

Hint: Use int main() with return 0 and correct loop range [OK]

Common Mistakes:

• Using void main() instead of int main()
• Incorrect loop range (less than 5)
• Omitting return statement
• Missing braces causing confusion