By default variables become internal implicitly when an assignment (or FOR statement) marks the first use of the variable in a piece of CalcIt code. If we want explicitly to make variables internal then we can use INTERN command. This command takes, as parameter, a list of variables separated by commas. These variables will become internal.
All normal variables (if not defined before) are initialized to empty string. Note that empty string is equivalent to zero in numeric operations.
Also we can declare array variables if we precede the array variable with the keyword arr. Arrays declared this way (if not defined before) are initialized with zero elements.
The above declares normal variables a, b, c and the array variable ArVar.
See also EXTERN