Format Specifiers in C

A format specifier is a special sequence beginning with % that tells a formatted I/O function how to interpret an argument.

printf("%d", age);

Here, %d tells printf() to format the corresponding argument as an integer.

Format specifiers are useful because they tell formatted input and output functions what type of data is being processed.

• Display integer values.
• Display floating-point values.
• Display characters.
• Read values using scanf().
• Control the appearance of formatted output.

The %d conversion specifier is commonly used with an int value.

int age = 20;

printf("%d", age);

Output:

20

The %i conversion specifier can also be used with an integer argument in printf().

int number = 100;

printf("%i", number);

In scanf(), %i has additional behavior: the input base can be detected from prefixes such as 0 or 0x.

The %u conversion specifier is used for an unsigned integer.

unsigned int count = 50;

printf("%u", count);

The %f conversion specifier is used to format a double argument in printf(). A float argument is automatically promoted to double when passed to printf().

float price = 99.50f;

printf("%f", price);

When using scanf(), %lf is used to read a double.

double salary;

scanf("%lf", &salary);

The & provides the address where the input value should be stored.

In scanf(), %f is used to read a float.

float price;

scanf("%f", &price);

The %c conversion specifier is used for a single character.

char grade = 'A';

printf("%c", grade);

Output:

A

The %s conversion specifier is used to print a null-terminated string.

char name[] = "Rahul";

printf("%s", name);

Output:

Rahul

The %x conversion specifier displays an unsigned integer in lowercase hexadecimal notation.

int number = 255;

printf("%x", number);

Output:

ff

The %X conversion specifier displays an unsigned integer in uppercase hexadecimal notation.

int number = 255;

printf("%X", number);

Output:

FF

The %o conversion specifier displays an unsigned integer in octal notation.

int number = 64;

printf("%o", number);

Output:

100

The %e conversion specifier displays a floating-point value using scientific notation with a lowercase e.

double number = 12345.67;

printf("%e", number);

The %E conversion specifier is similar to %e, but uses an uppercase E in the exponent.

double number = 12345.67;

printf("%E", number);

The %g conversion specifier chooses between normal floating-point notation and scientific notation, using the more appropriate representation for the value and precision.

double number = 123.456;

printf("%g", number);

The sequence %% is used in printf() to display a percent sign.

printf("Success: 90%%");

Output:

Success: 90%

A field width can be used to specify a minimum number of character positions for formatted output.

printf("%5d", 25);

The value is printed in a field with a minimum width of 5 characters.

Precision can control the number of digits displayed after the decimal point when using printf() with %f.

double price = 99.5678;

printf("%.2f", price);

Output:

99.57

The - flag can left-align a value within the specified field width.

printf("%-10d", 25);

This places the value toward the left side of a field of at least 10 characters.

The 0 flag can be used to pad certain numeric output with zeros.

printf("%05d", 25);

Output:

00025

The l length modifier can be used with d to format a long int.

long int population = 1000000L;

printf("%ld", population);

The ll length modifier can be used with d for a long long int.

long long int number = 9000000000LL;

printf("%lld", number);

The %lu conversion specification can be used to format an unsigned long value.

unsigned long population = 1000000UL;

printf("%lu", population);

The %zu conversion specification is used with a size_t value, such as the result of sizeof.

printf("%zu", sizeof(int));

This is the standard way to print a size_t value.

The scanf() function also uses format specifiers to determine what kind of input should be read.

int age;

scanf("%d", &age);

The address operator & is commonly used with scalar variables so that scanf() can store the input value.

char grade;

scanf(" %c", &grade);

The space before %c tells scanf() to skip leading whitespace characters such as a leftover newline.

For a character array, %s can read a word until whitespace is encountered.

char name[20];

scanf("%19s", name);

The width limit helps prevent input from exceeding the array's capacity.

#include <stdio.h>

int main()
{
    int age = 20;
    unsigned int students = 50;
    float percentage = 85.5f;
    double salary = 25000.75;
    char grade = 'A';
    char name[] = "Rahul";

    printf("Name = %s\n", name);
    printf("Age = %d\n", age);
    printf("Students = %u\n", students);
    printf("Percentage = %.1f\n", percentage);
    printf("Salary = %.2f\n", salary);
    printf("Grade = %c\n", grade);
    printf("Hex = %x\n", age);

    return 0;
}

This example demonstrates several commonly used format specifiers with different types of data.