Using printf for output in C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of printf with mixed format specifiers

What is the output of the following C code?

C

#include <stdio.h>

int main() {
    int a = 5;
    float b = 3.2f;
    printf("%d %.1f\n", a, b);
    return 0;
}

A 5 3

B 5.0 3.2

C 5 3.20

D 5 3.2

💡 Hint

Look at the format specifiers %d and %.1f and how they control output.

The %d prints the integer 5 as '5'. The %.1f prints the float with one decimal place, so 3.2 is printed as '3.2'.

❓ Predict Output

intermediate

Output of printf with escape sequences

What will this C program print?

C

#include <stdio.h>

int main() {
    printf("Hello\nWorld\t!\n");
    return 0;
}

A

Hello
World    !

B

Hello
World	!

C Hello World !

D HelloWorld!\n

💡 Hint

Remember \n is new line and \t is tab (spaces).

The \n creates a new line, so 'Hello' and 'World' appear on separate lines. The \t adds a tab space before '!'.

🔧 Debug

advanced

Identify the error in printf usage

What error will this code produce when compiled or run?

C

#include <stdio.h>

int main() {
    int x = 10;
    printf("Value is %d %f", x);
    return 0;
}

A Compilation error: missing argument for %f

B Runtime error: segmentation fault

C Output: Value is 10 (garbage value)

D Output: Value is 10 0.000000

💡 Hint

Check how many arguments printf expects vs provided.

The format string expects two arguments (%d and %f), but only one (x) is provided. This causes undefined behavior and prints garbage for %f.

🧠 Conceptual

advanced

Understanding printf return value

What does the printf function return after printing successfully?

A Always zero

B The number of characters printed

C The last character printed

D A pointer to the output string

💡 Hint

Think about what information printf might give back after printing.

printf returns the number of characters it successfully printed to the output.

📝 Syntax

expert

Which printf statement compiles and prints correctly?

Choose the option that compiles without error and prints exactly: 3.14

A printf("%.2f", 3.14159);

B printf("%2.f", 3.14159);

C printf("%f.2", 3.14159);

D printf("%.2d", 3.14159);

💡 Hint

Check the correct syntax for floating point precision in printf.

Option A uses %.2f which prints a float with 2 decimal places. Others have syntax errors or wrong specifiers.

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