Structure of a C program - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple C program with main function

What is the output of this C program when compiled and run?

C

#include <stdio.h>

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

A hello, c world!

B Hello, C world!\n

C Hello, C world!

D Compilation error

💡 Hint

Look carefully at the exact string printed and the newline character.

The program prints exactly "Hello, C world!" followed by a newline, so the output is that text on one line.

❓ Predict Output

intermediate

Value of variable after execution

What is the value of variable x after running this program?

C

#include <stdio.h>

int main() {
    int x = 5;
    x = x + 10;
    return 0;
}

A 5

B 10

C Compilation error

D 15

💡 Hint

x starts at 5 and then 10 is added.

x is initialized to 5, then 10 is added, so x becomes 15.

❓ Predict Output

advanced

Output of a program with multiple functions

What is the output of this C program?

C

#include <stdio.h>

void greet() {
    printf("Hi! ");
}

int main() {
    greet();
    printf("Welcome to C programming.\n");
    return 0;
}

A Hi! Welcome to C programming.\n

B Hi! Welcome to C programming.

C .gnimmargorp C ot emocleW !iH

D i! Welcome to C programming.

E Compilation error

💡 Hint

Look at how printf handles newlines.

The greet function prints "Hi! " without newline, then main prints the rest with newline, so output is on one line with newline at end.

❓ Predict Output

advanced

What error does this program produce?

What error will this C program produce when compiled?

C

#include <stdio.h>

int main() {
    int a = 10
    printf("Value: %d\n", a);
    return 0;
}

A Syntax error: missing semicolon

B No error, prints 'Value: 10'

C Runtime error: undefined variable

D Linker error: missing main

💡 Hint

Check each line for missing punctuation.

The line 'int a = 10' is missing a semicolon at the end, causing a syntax error.

🧠 Conceptual

expert

Number of functions in this C program

How many functions are defined in this C program?

C

#include <stdio.h>

void first() {
    printf("First\n");
}

void second() {
    printf("Second\n");
}

int main() {
    first();
    second();
    return 0;
}

A 3

B 2

C 4

D 1

💡 Hint

Count all functions including main.

There are three functions: first, second, and main.

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