Format specifiers

Introduction

Format specifiers tell the computer how to show or read different types of data like numbers or letters.

When you want to print a number or text on the screen in C.

When you need to read input from the user and store it correctly.

When you want to format output neatly, like showing decimals or padding spaces.

Syntax

C

printf("format_specifier", value);
scanf("format_specifier", &variable);

Format specifiers start with % and tell how to display or read data.

Common specifiers include %d for integers, %f for floating-point numbers, and %c for characters.

Examples

Prints the integer 10.

C

printf("%d", 10);

Prints the floating-point number 3.14.

C

printf("%f", 3.14);

Reads a single character from user input into variable ch.

C

scanf("%c", &ch);

Prints the string 'Hello World'.

C

printf("Hello %s", "World");

Sample Program

This program prints an integer, a floating-point number with one decimal, and a character using format specifiers.

C

#include <stdio.h>

int main() {
    int age = 25;
    float height = 5.9f;
    char initial = 'J';

    printf("Age: %d\n", age);
    printf("Height: %.1f feet\n", height);
    printf("Initial: %c\n", initial);

    return 0;
}

Important Notes

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

You can control decimal places with %.nf where n is the number of decimals.

Always use & before variable names in scanf to store input correctly.

Summary

Format specifiers tell C how to print or read data.

Common specifiers: %d (int), %f (float), %c (char), %s (string).

Use them in printf to show data and scanf to get data.

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