main function and program entry - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the main function in C.

C

int [1]() {
    return 0;
}

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

Amain

Bstart

Cbegin

Dinit

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function name other than 'main' for the program entry point.

Forgetting to specify the return type as int.

The main function in C must be named main. This is where the program starts running.

2fill in blank

medium

Complete the code to print "Hello, World!" inside the main function.

C

#include <stdio.h>

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

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

Aprint

Bprintln

Cecho

Dprintf

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'print' which is not a C function.

Using 'echo' or 'println' which are not valid in C.

In C, printf is used to print formatted output to the screen.

3fill in blank

hard

Fix the error in the main function declaration to make it valid C code.

C

int [1](void) {
    return 0;
}

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

Aprogram

Bmain

Cstart

Dentry

Attempts:

3 left

💡 Hint

Common Mistakes

Using other function names like 'start' or 'entry' instead of 'main'.

The main function must be named main to be recognized as the program entry point.

4fill in blank

hard

Fill both blanks to complete the main function that prints a number.

C

#include <stdio.h>

int [1]() {
    int num = 5;
    [2]("Number: %d\n", num);
    return 0;
}

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

Amain

Bprint

Cprintf

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'print' instead of 'printf'.

Naming the function other than 'main'.

The program starts with the main function and uses printf to print formatted output.

5fill in blank

hard

Fill all three blanks to complete a main function that prints a message and returns success.

C

#include <stdio.h>

int [1]() {
    [2]("Welcome to C programming!\n");
    return [3];
}

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

Amain

Bprintf

C0

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Returning a non-zero value to indicate success.

Using a function name other than 'main'.

The main function is named 'main', uses 'printf' to print, and returns 0 to indicate success.

Practice

1. What is the role of the main function in a C program?

easy

A. It stores all the variables used in the program.

B. It handles input and output operations automatically.

C. It compiles the program into machine code.

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

Solution

1. Step 1: Understand program execution start

   The main function is where the computer starts running the program.

2. Step 2: Identify the role of main

   It acts as the entry point, so the program begins here.

3. Final Answer:

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

4. Quick Check:

   Program entry = main function [OK]

Hint: Remember: main is where the program starts running [OK]

Common Mistakes:

• Thinking main stores variables
• Confusing main with compilation process
• Assuming main handles all input/output automatically

2. Which of the following is the correct syntax to declare the main function in C?

easy

A. int main()

B. void main()

C. main int()

D. main() int

Solution

1. Step 1: Recall standard main function syntax

   The standard and portable way is to declare main returning an integer: int main().

2. Step 2: Check each option

   void main() uses void which is not standard. Options C and D have incorrect order and syntax.

3. Final Answer:

   int main() -> Option A

4. Quick Check:

   Standard main syntax = int main() [OK]

Hint: Main should return int, so use int main() [OK]

Common Mistakes:

• Using void main() which is non-standard
• Writing main int() or main() int which is invalid syntax
• Omitting return type

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

#include <stdio.h>
int main() {
    printf("Hello, World!\n");
    return 0;
}

medium

A. No output

B. Hello, World!

C. 0

D. Compilation error

Solution

1. Step 1: Analyze the printf statement

   The program prints the string "Hello, World!" followed by a newline.

2. Step 2: Check return value effect

   The return 0; ends the program successfully but does not print anything.

3. Final Answer:

   Hello, World! -> Option B

4. Quick Check:

   printf prints text = Hello, World! [OK]

Hint: printf prints text; return 0 ends program silently [OK]

Common Mistakes:

• Confusing return 0 with printed output
• Expecting 0 to print automatically
• Thinking no output because of return 0

4. Identify the error in this C program:

#include <stdio.h>
int main() {
    printf("Start\n")
    return 0;
}

medium

A. Missing #include directive

B. Incorrect return type of main

C. Missing semicolon after printf statement

D. main function should return void

Solution

1. Step 1: Check syntax of printf line

   The printf statement lacks a semicolon at the end, which is required in C.

2. Step 2: Verify other parts

   The return type is correct, #include is present, and main returns int as expected.

3. Final Answer:

   Missing semicolon after printf statement -> Option C

4. Quick Check:

   Statements must end with ; = missing semicolon [OK]

Hint: Every statement ends with ; in C [OK]

Common Mistakes:

• Forgetting semicolon after function calls
• Changing main return type incorrectly
• Removing #include directive

5. You want your C program to indicate successful completion to the operating system. Which statement should you include at the end of main?

hard

A. return 0;

B. exit(0);

C. void main();

D. return 1;

Solution

1. Step 1: Understand return value meaning

   Returning 0 from main signals successful program completion to the OS.

2. Step 2: Evaluate options

   return 1; returns 1 which usually means error. exit(0); calls exit but is less common in simple main. void main(); is invalid syntax.

3. Final Answer:

   return 0; -> Option A

4. Quick Check:

   Success signal = return 0; [OK]

Hint: Use return 0; to say program ended well [OK]

Common Mistakes:

• Using return 1; which signals error
• Confusing exit(0) with return 0;
• Writing void main(); which is invalid