Format Specifiers in C

The format specifier in C is used to tell the compiler about the type of data to be printed or scanned in input and output operations. They always start with a % symbol and are used in the formatted string in functions like printf(), scanf, sprintf(), etc.

The C language provides a number of format specifiers that are associated with the different data types such as %d for int, %c for char, etc. In this article, we will discuss some commonly used format specifiers and how to use them.

List of Format Specifiers in C

The below table contains the most commonly used format specifiers in C

Format Specifier	Description
%c	For character type.
%d	For signed integer type.
%e or %E	For scientific notation of floats.
%f	For float type.
%g or %G	For float type with the current precision.
%i	Unsigned integer
%ld or %li	Long
%lf	Double
%Lf	Long double
%lu	Unsigned int or unsigned long
%lli or %lld	Long long
%llu	Unsigned long long
%o	Octal representation
%p	Pointer
%s	String
%u	Unsigned int
%x or %X	Hexadecimal representation
%n	Prints nothing
%%	Prints % character

Examples of Format Specifiers in C

1. Character Format Specifier – %c in C

The %c is the format specifier for the char data type in C language. It can be used for both formatted input and formatted output in C language.

Syntax:

scanf("%d...", ...);
printf("%d...", ...);

Example:

C

// C Program to illustrate the %c format specifier.
#include <stdio.h>

int main()
{

    char c;
    // using %c for character input
    scanf("Enter some character: %c", &c);

    // using %c for character output
    printf("The entered character: %c", &c);
    return 0;
}

Input:

Enter some character: A

Output:

The entered character: A

2. Integer Format Specifier (signed) – %d in C

We can use the signed integer format specifier %d in the scanf() and print() functions or other functions that use formatted string for input and output of int data type.

Syntax:

scanf("%d...", ...);
printf("%i...", ...);

Example:

C

// C Program to demonstrate the use of %d and %i
#include <stdio.h>

// Driver code
int main()
{
    int x;
    // taking integer input
    scanf("Enter the two integers: %d", &x);

    // printing integer output
    printf("Printed using %%d: %d\n", x);
    printf("Printed using %%i: %3i\n", x);
    return 0;
}

Input:

Enter the integer: 45

Output:

Printed using %d: 45
Printed using %i:    45

3. Unsigned Integer Format Specifier –  %u in C

The %u is the format specifier for the unsigned integer data type. If we specify a negative integer value to the %u, it converts the integer to its first complement.

Syntax:

printf("%u...", ...);
scanf("%u...", ...);

Example: The following C Program demonstrates how to use %u in C.

C

// C Program to illustrate the how to use %u
#include <stdio.h>

// driver code
int main()
{
    unsigned int var;

    scanf("Enter an integer: %u", &var);

    printf("Entered Unsigned Integer: %u", var);

    // trying to print negative value using %u
    printf("Printing -10 using %%u: %u\n", -10);
    return 0;
}

Input:

Enter an integer: 25

Output:

Entered unsigned integer: 25
Printing -10 using %u: 4294967286

4. Floating-point format specifier – %f in C

The %f is the floating point format specifier in C language that can be used inside the formatted string for input and output of float data type. Apart from %f, we can use %e or %E format specifiers to print the floating point value in the exponential form.

Syntax:

printf("%f...", ...);
scanf("%e...", ...);
printf("%E...", ...);

Example:

C

// C program to demonstrate the use of %f, %e  and %E
#include <stdio.h>

// driver code
int main()
{
    float a = 12.67;
    printf("Using %%f: %f\n", a);
    printf("Using %%e: %e\n", a);
    printf("Using %%E, %E", a);
    return 0;
}

Output

Using %f: 12.670000
Using %e: 1.267000e+01
Using %E, 1.267000E+01

5. Unsigned Octal number for integer – %o in C

We can use the %o format specifier in the C program to print or take input for the unsigned octal integer number.

Syntax:

printf("%o...", ...);
scanf("%o...", ...);

Example:

C

#include <stdio.h>
int main()
{
    int a = 67;
    printf("%o\n", a);
    return 0;
}

Output

103

6. Unsigned Hexadecimal for integer – %x in C

The %x format specifier is used in the formatted string for hexadecimal integers. In this case, the alphabets in the hexadecimal numbers will be in lowercase. For uppercase alphabet digits, we use %X instead.

Syntax:

printf("%x...", ...);
scanf("%X...", ...);

Example:

C

// C Program to demonstrate the use of %x and %X
#include <stdio.h>
int main()
{
    int a = 15454;
    printf("%x\n", a);
    printf("%X", a);
    return 0;
}

Output

3c5e
3C5E

7. String Format Specifier – %s in C

The %s in C is used to print strings or take strings as input.

Syntax:

printf("%s...", ...);
scanf("%s...", ...);

Example:

C

// C program to illustrate the use of %s in C
#include <stdio.h>

int main()
{
    char a[] = "Hi Geeks";
    printf("%s\n", a);
    return 0;
}

Output

Hi Geeks

Example: The working of %s with scanf() is a little bit different from its working with printf(). Let’s understand this with the help of the following C program.

C

// C Program to illustrate the working of %s with scanf()
#include <stdio.h>

int main()
{

    char str[50];
    // taking string as input
    scanf("Enter the String: %s", str);

    printf("Entered String: %s", str);

    return 0;
}

Input

Enter the string: Hi Geeks

Output

Hi

As we can see, the string is only scanned till a whitespace is encountered. We can avoid that by using scansets in C.

8. Address Format Specifier – %p in C

The C language also provides the format specifier to print the address/pointers. We can use %p to print addresses and pointers in C

Syntax

printf("%p...", ...);

Example:

C

#include <stdio.h>
int main()
{
    int a = 10;
    printf("The Memory Address of a: %p\n",(void*)&a);
    return 0;
}

Output

The Memory Address of a: 0x7ffe9645b3fc

Input and Output Formatting

C language provides some tools using which we can format the input and output. They are generally inserted between the % sign and the format specifier symbol Some of them are as follows:

1. A minus(-) sign tells left alignment.
2. A number after % specifies the minimum field width to be printed if the characters are less than the size of the width the remaining space is filled with space and if it is greater then it is printed as it is without truncation.
3. A period( . ) symbol separates field width with precision.

Precision tells the minimum number of digits in an integer, the maximum number of characters in a string, and the number of digits after the decimal part in a floating value.

Example of I/O Formatting

C

// C Program to demonstrate the formatting methods.
#include <stdio.h>
int main()
{
    char str[] = "geeksforgeeks";
    printf("%20s\n", str);
    printf("%-20s\n", str);
    printf("%20.5s\n", str);
    printf("%-20.5s\n", str);
    return 0;
}

Output

       geeksforgeeks
geeksforgeeks       
               geeks
geeks               

FAQs on C Format Specifiers

1. Does C have a format specifier for binary numbers?

No, the C language does not provide a format specifier for binary numbers.

2. What is the formatted string?

The input and output functions in C take a string as an argument that decides how the data is displayed on the screen or the data is retrieved to the memory. This string is called the formatted string.