Constants, Variables and Keywords

Constants, Variables and Keywords
The alphabets, numbers and special symbols when properly combined form  constants, variables and keywords. Let us  see  what are ‘constants’  and ‘variables’  in  C.  A constant is an entity  that doesn’t  change whereas a variable is an entity  that  may  change. In any  program  we  typically  do lots of calculations. The results of these calculations are stored in computers memory. Like human memory  the  computer memory  also  consists  of  millions of cells. The calculated values are stored in these memory  cells. To make the retrieval and usage  of these values easy these memory  cells (also called  memory  locations) are given names. Since the value stored in each location may  change the names  given to these locations are called variable names.
Consider the following example:  Here 3 is stored in a  memory  location and a name  x  is given to it. Then we are  assigning a new value 5 to the same  memory  location x. This would overwrite  the earlier  value 3, since a memory location can hold only  one value at a time. Since the location whose name  is  x  can hold different values at different times  x  is known as a  variable. As against this, 3  or 5  do not change,  hence are known as constants.