DATATYPE( )

When attempting to perform arithmetic on data entered from the keyboard, you can use the DATATYPE( ) function to check that the data is valid.

This function has several forms. The simplest form returns the word, NUM, if the expression inside the parentheses ( ) is accepted by the interpreter as a number that can be used in the arithmetic operation. Otherwise, it returns the word, CHAR. For example: 

The value of DATATYPE(56) is NUM
The value of DATATYPE(6.2) is NUM
The value of DATATYPE('$5.50') is CHAR
In the following procedure, DATATYPE.CMD, the internal REXX function, DATATYPE( ), is used and the user is asked to keep typing a valid number until a correct one is typed. 
/* Using the DATATYPE( ) Function */
DO UNTIL datatype(howmuch) = 'NUM'
 SAY 'Enter a number'
 PULL howmuch
  IF datatype (howmuch) = 'CHAR'
   THEN
   SAY 'That was not a number.  Try again!'
END
SAY 'The number you entered was' howmuch
EXIT

If you want the user to type only whole numbers, you could use another form of the DATATYPE( ) function: 

DATATYPE (number, whole)

The arguments for this form are: