Using printf for output in C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print the text "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

Bprint

Ccout

Decho

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'print' which is not a C function.

Using 'cout' which is from C++.

Using 'echo' which is from shell scripting.

The printf function is used in C to print formatted output to the screen.

2fill in blank

medium

Complete the code to print the integer variable 'num' using printf.

C

#include <stdio.h>

int main() {
    int num = 10;
    printf("[1]\n", num);
    return 0;
}

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

A%f

B%d

C%s

D%c

Attempts:

3 left

💡 Hint

Common Mistakes

Using %s which is for strings.

Using %f which is for floating-point numbers.

Using %c which is for characters.

The format specifier %d is used to print integers in C.

3fill in blank

hard

Fix the error in the printf statement to correctly print a float variable 'pi'.

C

#include <stdio.h>

int main() {
    float pi = 3.14;
    printf("Value of pi: [1]\n", pi);
    return 0;
}

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

A%c

B%s

C%d

D%f

Attempts:

3 left

💡 Hint

Common Mistakes

Using %d which is for integers.

Using %s which is for strings.

Using %c which is for characters.

The format specifier %f is used to print floating-point numbers in C.

4fill in blank

hard

Fill both blanks to print a character and an integer using printf.

C

#include <stdio.h>

int main() {
    char letter = 'A';
    int number = 5;
    printf("Character: [1], Number: [2]\n", letter, number);
    return 0;
}

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

A%c

B%d

C%f

D%s

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping %c and %d.

Using %f or %s incorrectly.

%c prints a character and %d prints an integer in C.

5fill in blank

hard

Fill all three blanks to print a string, an integer, and a float using printf.

C

#include <stdio.h>

int main() {
    char name[] = "Bob";
    int age = 25;
    float height = 5.9;
    printf("Name: [1], Age: [2], Height: [3]\n", name, age, height);
    return 0;
}

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

A%d

B%s

C%f

D%c

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up format specifiers.

Using %c for strings or floats.

%s prints strings, %d prints integers, and %f prints floats in C.

Practice

1. What does the printf function do in C?

easy

A. It reads input from the keyboard.

B. It saves data to a file.

C. It displays text or values on the screen.

D. It performs mathematical calculations.

Solution

1. Step 1: Understand the purpose of printf

   The printf function is used to show messages or values on the screen in C programs.

2. Step 2: Compare options with the function's purpose

   Only It displays text or values on the screen. correctly describes printf as displaying output. Other options describe different functions.

3. Final Answer:

   It displays text or values on the screen. -> Option C

4. Quick Check:

   printf = output display [OK]

Hint: printf always prints output to the screen [OK]

Common Mistakes:

• Confusing printf with input functions like scanf
• Thinking printf saves data to files
• Assuming printf does calculations

2. Which of the following is the correct syntax to print an integer variable num using printf?

easy

A. printf("%d", num);

B. printf("%s", num);

C. printf(num);

D. printf("num");

Solution

1. Step 1: Identify the correct placeholder for integer

   The placeholder for integers in printf is %d.

2. Step 2: Match syntax with variable and placeholder

   printf("%d", num); uses %d and passes num correctly. Other options use wrong placeholders or incorrect syntax.

3. Final Answer:

   printf("%d", num); -> Option A

4. Quick Check:

   Integer placeholder = %d [OK]

Hint: Use %d for integers in printf [OK]

Common Mistakes:

• Using %s for integers
• Passing variable without placeholder
• Putting variable name in quotes

3. What is the output of this code?

int x = 5;
printf("Value: %d\n", x);

medium

A. x

B. Value: %d

C. Value:

D. Value: 5

Solution

1. Step 1: Understand the printf statement

   The placeholder %d is replaced by the value of x, which is 5.

2. Step 2: Consider the newline character

   The \n moves the cursor to the next line after printing.

3. Final Answer:

   Value: 5 -> Option D

4. Quick Check:

   Placeholder %d replaced by 5 [OK]

Hint: Placeholders show variable values in output [OK]

Common Mistakes:

• Printing the placeholder text instead of value
• Ignoring newline character
• Printing variable name instead of value

4. Find the error in this code snippet:

int a = 10;
printf("The value is %d", a)

medium

A. Wrong placeholder used for integer.

B. Missing semicolon after printf statement.

C. Variable 'a' is not declared.

D. printf cannot print integers.

Solution

1. Step 1: Check syntax of printf statement

   The printf line is missing a semicolon at the end, which is required in C.

2. Step 2: Verify other parts

   The placeholder %d is correct for integer, and variable a is declared properly.

3. Final Answer:

   Missing semicolon after printf statement. -> Option B

4. Quick Check:

   Every statement ends with ; in C [OK]

Hint: Check for missing semicolons after statements [OK]

Common Mistakes:

• Forgetting semicolon after printf
• Using wrong placeholder for data type
• Not declaring variables before use

5. You want to print a floating-point number pi with 2 decimal places using printf. Which code is correct?

hard

A. printf("%.2f", pi);

B. printf("%2f", pi);

C. printf("%f.2", pi);

D. printf("%f", pi, 2);

Solution

1. Step 1: Understand floating-point formatting

   To print a float with 2 decimals, use %.2f in printf.

2. Step 2: Check each option's correctness

   printf("%.2f", pi); uses %.2f correctly. printf("%2f", pi); misses the dot, C has wrong syntax, D passes extra argument incorrectly.

3. Final Answer:

   printf("%.2f", pi); -> Option A

4. Quick Check:

   Use %.2f for 2 decimal float output [OK]

Hint: Use %.2f to limit float decimals to 2 [OK]

Common Mistakes:

• Omitting the dot before precision
• Passing extra arguments to printf
• Using wrong placeholder format