Format specifiers - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a format specifier in C?

A format specifier is a special sequence in a string that tells the program how to display or read data, like %d for integers or %f for floating-point numbers.

beginner

What does the format specifier %d represent?

The %d specifier is used to print or read an integer (whole number) value.

intermediate

How do you print a floating-point number with 2 decimal places in C?

Use %.2f in the format string. For example, printf("%.2f", 3.14159) prints 3.14.

beginner

What format specifier is used to print a single character?

The %c specifier is used to print a single character.

beginner

How do you print a string in C using format specifiers?

Use %s to print a string. For example, printf("%s", "hello") prints hello.

Which format specifier is used to print an integer in C?

A %d

B %f

C %c

D %s

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

How would you print the floating-point number 3.14159 with 3 decimal places?

A %d

B %3f

C %f.3

D %.3f

Use %.3f to specify 3 decimal places for a float.

What does the format specifier %c print?

A A character

B A string

C An integer

D A floating-point number

%c prints a single character.

Which format specifier is used to print a string?

A %d

B %c

C %s

D %f

%s is used to print strings.

What will printf("%5d", 42); print?

A An error

B 42 with 5 spaces before it

C 42 with no spaces

D 42 with 5 spaces after it

The %5d specifier prints the integer right-aligned in a field 5 characters wide, adding spaces before the number.

Explain what format specifiers are and give three examples with their uses.

Think about how you tell the program to print different types of data.

Describe how to control the number of decimal places when printing a floating-point number in C.

Focus on the dot and number inside the format specifier.

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