Constant
1,2.0,O22,Ox1a (integer constants,decimal,octal, hexadecimal); 1.0, 3.14 (floating constants); 'a','1' (character constants); '\n','\a' (special character constant: newline,bell); and enumeration constant (enum boolean {FALSE, TRUE});"1997" (string constant); NULL (pointer constant)
-23 (constant expression: operator '-' with operand 23)
names can be given to constants by using the preprocessor directive #define