Difference Between Variable and Constant
Variable is a mathematical value which can change within the limit of a given problem or a combination of operation. On the other hand, constant refers to a value which remains fixed or unchanged and is often undetermined and unknown. Both the terms have emerged from mathematical studies and have great significance in the many fields. A mathematical constant is a specific number which is usually a real number.
Variables can further be divided into dependent and independent variables. Independent variables are those variables which are not affected by a change in any other variable and used as inputs in any system. In contrast, dependent variables are those variables which change because of a change in some other values in a system.
Instructions

1
Variable
In mathematics, variable is referred to a term which keeps on changing within its limitations and can take up any value as a consequence of any change in the scenario. Some variables are independent and some are dependent. Variables have great significance in algebra and other fields of mathematics. Moreover, they are widely used in other fields of knowledge.
Variables are most commonly used in research conducted at different levels. The research can be basic or applied. The sophistication of theoretical framework in the research depend on the effectiveness of the variables used in it and their relationship with each other. The researcher defines the variables in research according to his senses after going through the literature and develops a theory which is later testified. Mostly, the research is conducted with dependent and independent variables, but sometimes, a researcher introduces an intervening or moderating variable in his study to make his theoretical framework more precise and sophisticated.
 Image courtesy: vimeo.com

2
Constant
It refers to a specific number and remains unchanged within the given problem. The most common mathematical constants include value of ‘e’ and Archimedes constant i.e. pi which are used in geometry, calculus and number theory. It is very important for you to keep in mind that all the mathematical constants are numbers which can be defined easily and are computable. The constants are represented by different symbols. However, they can be written as simple values also. The constants are also extensively used in physics, computer programming and logical reasoning.
 Image courtesy: festivaldelsole.org