In this post I want to create a helpful reference for all the C conversion specifiers you can use, commonly with printf(), scanf() and similar I/O functions.

Specifier	Meaning
%d / %i	Signed decimal integer
%u	Unsigned decimal integer
%c	Unsigned char
%s	String
%p	Pointer in hexadecimal form
%o	Unsigned octal integer
%x / %X	Unsigned hexadecimal number
%e	Floating point number in exponential format in e notation
%E	Floating point number in exponential format in E notation
%f	double number in decimal format
%g / %G	double number in decimal format or exponential format depending on the value

In addition to those specifiers, we have a set of modifiers.

Let’s start with digits. Using a digit between % and the format specifier, you can tell the minimum field width. Example: %3d will take 3 spaces regardless of the number printed.

This:

printf("%4d\n", 1);
printf("%4d\n", 12);
printf("%4d\n", 123);
printf("%4d\n", 1234);

should print

   1
  12
 123
1234

If you put a dot before the digit, you are not telling the precision: the number of decimal digits. This of course applies to decimal numbers. Example:

printf("%4.2f\n", 1.0);
printf("%4.3e\n", 12.232432442);
printf("%4.1e\n", 12.232432442);
printf("%4.1f\n", 123.22);

will print:

1.00
1.223e+01
1.2e+01
123.2

In addition to digits, we have 3 special letters: h, l and L.

• h, used with integer numbers, indicates a short int (for example %hd) or a short unsigned int (for example %hu)
• l, used with integer numbers, indicates a long int (for example %ld) or a long unsigned int (for example %lu).
• L, used with floating point numbers, indicates a long double, for example %Lf

Lessons in this unit:

0:	Introduction
1:	Input and output
2:	Variable scope
3:	Static variables
4:	Global variables
5:	Type definitions
6:	Enumerations
7:	Structures
8:	Command line parameters
9:	Header files
10:	The preprocessor
11:	NULL values
12:	Boolean values
13:	Nesting functions
14:	▶︎ Conversion specifiers
15:	Using quotes
16:	String length
17:	Returning strings
18:	Array length
19:	Looping through arrays
20:	Checking character values
21:	Printing percentage signs
22:	Troubleshooting: Implicit function declarations