Format specifiers - Mini Project: Build & Apply

Format Specifiers in C

📖 Scenario: You are creating a simple program to display different types of data about a product in a store. You will learn how to use format specifiers to print integers, floating-point numbers, and characters correctly.

🎯 Goal: Build a C program that stores product details and prints them using the correct format specifiers.

📋 What You'll Learn

Create variables with exact names and values

Use correct format specifiers for each variable type

Print the output exactly as instructed

💡 Why This Matters

🌍 Real World

Format specifiers are used in many programs to display data clearly, such as showing prices, IDs, or grades in reports or user interfaces.

💼 Career

Understanding format specifiers is essential for C programming jobs, especially in systems programming, embedded systems, and any application that requires formatted text output.

1

Create product data variables

Create three variables with these exact names and values: product_id as integer 101, price as float 29.99, and grade as character 'A'.

C

# Create variables product_id, price, and grade with given values
// Your code here

Hint

Use int for whole numbers, float for decimal numbers, and char for single characters.

2

Add a format string variable

Create a variable called format_str of type char* and set it to the string "ID: %d, Price: %.2f, Grade: %c".

C

int product_id = 101;
float price = 29.99f;
char grade = 'A';
// Create format_str with the exact format string
// Your code here

Hint

Use char* to store a string and include the exact format specifiers for integer, float with 2 decimals, and character.

3

Print product details using format specifiers

Write a printf statement using format_str to print product_id, price, and grade in that order.

C

int product_id = 101;
float price = 29.99f;
char grade = 'A';
char* format_str = "ID: %d, Price: %.2f, Grade: %c";
// Print the product details using printf and format_str
// Your code here

Hint

Use printf with the format string and variables in the correct order.

4

Display the output

Run the program and print the output exactly as: ID: 101, Price: 29.99, Grade: A

C

int product_id = 101;
float price = 29.99f;
char grade = 'A';
char* format_str = "ID: %d, Price: %.2f, Grade: %c";
printf(format_str, product_id, price, grade);
// Output is printed above

Hint

Make sure the output matches exactly, including spaces and punctuation.

Practice

1. Which format specifier is used to print an integer value in C using printf?

easy

A. %d

B. %f

C. %c

D. %s

Solution

1. Step 1: Understand integer data type printing

   The %d specifier is used to print integer values in C.

2. Step 2: Identify other specifiers

   %f is for floats, %c for characters, and %s for strings.

3. Final Answer:

   %d -> Option A

4. Quick Check:

   Integer print = %d [OK]

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

Common Mistakes:

• Using %f for integers
• Confusing %c with %d
• Using %s for numbers

2. Which of the following is the correct way to print a character variable ch in C?

easy

A. printf("%c", ch);

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

C. printf("%d", ch);

D. printf("%f", ch);

Solution

1. Step 1: Identify character format specifier

   The correct specifier for a character is %c.

2. Step 2: Check other options

   %s is for strings, %d for integers, and %f for floats, so they are incorrect for a character.

3. Final Answer:

   printf("%c", ch); -> Option A

4. Quick Check:

   Character print = %c [OK]

Hint: Use %c to print single characters [OK]

Common Mistakes:

• Using %s for characters
• Using %d which prints ASCII code
• Using %f for characters

3. What will be the output of the following code?

int x = 10;
float y = 5.5;
printf("%d %f", x, y);

medium

A. 10 5.5

B. 10 5.500000

C. 5.5 10

D. Error

Solution

1. Step 1: Understand format specifiers in printf

   %d prints integer as is, %f prints float with 6 decimal places by default.

2. Step 2: Match variables to specifiers

   x is 10 (int), printed by %d. y is 5.5 (float), printed by %f as 5.500000.

3. Final Answer:

   10 5.500000 -> Option B

4. Quick Check:

   Integer and float print with %d and %f [OK]

Hint: Floats print with 6 decimals by default using %f [OK]

Common Mistakes:

• Expecting %f to print fewer decimals
• Swapping variable order
• Using %d for float causing wrong output

4. Identify the error in the following code snippet:

char name[10];
scanf("%c", name);

medium

A. No error, code is correct

B. Use &name instead of name

C. Use %d instead of %c

D. Use %s instead of %c to read string

Solution

1. Step 1: Understand scanf format specifiers

   %c reads a single character, but name is an array for a string.

2. Step 2: Correct specifier for string input

   To read a string into name, use %s which reads until whitespace.

3. Final Answer:

   Use %s instead of %c to read string -> Option D

4. Quick Check:

   String input needs %s in scanf [OK]

Hint: Use %s to read strings with scanf [OK]

Common Mistakes:

• Using %c to read strings
• Forgetting & with non-array variables
• Using %d for characters

5. You want to print a floating-point number float pi = 3.14159; with only 2 decimal places. Which printf statement is correct?

hard

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

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

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

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

Solution

1. Step 1: Understand precision in format specifiers

   To limit decimal places, use %.2f where 2 is the number of decimals.

2. Step 2: Check other options

   %2f sets minimum width, not decimals; %f.2 is invalid; %f prints 6 decimals by default.

3. Final Answer:

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

4. Quick Check:

   Use %.2f to print 2 decimals [OK]

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

Common Mistakes:

• Using %2f expecting 2 decimals
• Placing .2 after %f incorrectly
• Using %f prints 6 decimals by default