Printf in C

printf() function is used to print formatted output in many ways to the standard output stdout(which is generally the console screen).

Syntax of printf

The printf() function is defined inside <stdio.h> header file.

printf("format_string", args...);

Parameter:

formatted_string: It's a string that specifies the data to be printed. It may also contain a format specifier as a placeholder to print the value of any variable or value.
args...: These are the variable/values corresponding to the format specifier.

Return Value:

Returns the numebr of characters printed after successful execution.
If an error occurs, a negative value is returned.

Format Specifier in printf

The format string inside printf() can include various format specifiers whose primary function is to act as a placeholder for printing the variables and values. These format specifiers start with the percentage symbol(%).

%[flags][width][.precision][length]specifier

Component	Meaning	Example
%	Marks the beginning of the specifier	%
flags	Adjust alignment, padding, symbols	-, +, 0, #,
width	Minimum field width	10, 4, etc.
.precision	Precision (decimal or min digits)	.2, .5, etc.
length	Length modifier (like long, short)	l, ll, h, z
specifier	Data type to print	d, f, s, x

1. flags

Flag	Description	Example
-	Left-align within the width	%-5d prints 42
+	Show sign for positive numbers	%+d prints +42, -42
0	Pad with zeros instead of spaces	%05d prints 00042
#	Add prefix (0x, 0) for hex/oct	%#x prints 0x2a
space	Add space before positive number if no +	% d prints 42

2. Width

It is the sub-specifier that denotes the minimum number of characters that will be printed.s

If the number of characters is less than the specified width, the white space will be used to fill the remaining characters' places.
But if the number of characters is greater than the specified width, all the characters will be still printed without cutting off any.

3. .Precision

Precision sub specifier meaning differs for different data types it is being used with.

For Integral data(d, i, u, o, x, X): Specifies the minimum number of digits to be printed. But unlike the width sub-specifier, instead of white spaces, this sub-specifier adds leading zeroes to the number. If the number has more digits than the precision, the number is printed as it is.
For Float or Double Data(f, e, a, A): Specifies the number of digits to be printed after the decimal point.
For String (s): Specifies the length of the string to be printed.

4. Length

There are 3 length sub-specifiers:

h: With short int and unsigned short int
l: With long int and unsigned long int.
L: With long double

Examples:

Right Align the Output

We can right align the output using the width specifier with positive value.

    char s[] = "Welcome to GfG!";

    // Printing right aligned string of width 40
    printf("%40s", s);

Output

text

                                                                                     Welcome to GfG!

Explanation: The format specifier %40s prints the string s right-aligned with a minimum width of 40 characters. If the string is shorter than 40 characters, it is padded with spaces on the left.

Left Align the Output with Specified Width

If we pass negative width, the minimum width will be the absolute value of the width, but the text will be left aligned.

↔
    char s[] = "Welcome to GfG!";

    // Printing left aligned string of width 50
    printf("%-50s", s);
    printf("Geeks");
↔

Output

text

Welcome to GfG!                                   Geeks

Explanation: The format specifier %-50s prints the string s left-aligned with a minimum width of 50 characters. The remaining spaces are padded with blanks, followed by printing Geeks.

Add Leading Zeroes to Integer

The precision sub-specifier adds leading zeroes to the integer.

↔
    int n = 2451;

    // Precision for integral data
    printf("%.10d
", n);
↔

Output

text

0000002451

Explanation: The format specifier %.10d ensures the integer n is printed with a precision of 10 digits. If n has fewer digits, it is left-padded with zeros to meet the required precision.

Limit Digits After Point in Float

For floating point values, precision limits the number of digits to be printed after decimal points.

↔
    float f = 2.451;

    // Precision for float data
    printf("%.2f", f);
↔

Output

text

2.45

**Explanation**: The format specifier **%.2f** ensures the floating-point number **f** is printed with **2** digits after the decimal point. It rounds the value if necessary.

Limit Number of Characters in a String

For strings, precision limits the number of characters to be printed.

↔
    char s[] = "Welcome to GfG!";

    // Print with 3 decimal places
    printf("%.7s", s);
↔

Output

text

Welcome

**Explanation:** The format specifier **%.7s** prints only the first **7** characters of the string **s**, truncating the rest if it exceeds this length.