In contrast to a variable, which is used as identifier for a value and which can change, constants are identifiers that are used for values, which cannot be changed. In other words constants are symbols used to refer to quantities which do not change throughout the life of a program. No assignment can be done to a constant. A numeric constant stands for a number. This number can be an integer, a decimal fraction, or a number in scientific (exponential) notation. Some of the operations which can be performed with numeric constants are addition, subtraction, multiplication, division and comparison. A string constant consists of a sequence of characters enclosed in double/single quote marks. Chopping off some of the characters from the beginning or end, adding another string at the end (concatenation), copying are some of the operations that performed on the string constants. All these operations can be done on variables also.