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15. INPUT STATEMENT

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15.1 General Description

Input-statements provide for user interaction with a running program by allowing variables to be assigned values that are supplied by a user. The input-statement enables the entry of mixed string and numeric data, with data items being separated by commas. The general syntactic form of the input-statement is


        INPUT variable, ..., variable

15.2 Syntax


            1. input-statement        = INPUT variable-list
            2. variable-list          = variable (comma variable)*
            3. input-prompt           = (implementation-defined) "? "
            4. input-reply            = input-list end-of-line
            5. input-list             = padded-datum (comma padded-datum)*
            6. padded-datum           = space* datum space*
            7. datum                  = quoted-string / unquoted-string

15.3 Examples


        INPUT X 3.14159 INPUT X, A$, Y(2) 2,SMITH,-3 INPUT A, B, C 25,0 ,-15

15.4 Semantics

An input-statement causes the variables in the variable-list to be assigned, in order, values from the input-reply. In the interactive mode, the user of the program is informed of the need to supply data by the output of an input-prompt. In batch mode, the input-reply is requested from the external source by an implementation-defined means. Execution of the program is suspended until a valid input-reply has been supplied. The type of each datum in the input-reply shall correspond to the type of the variable to which it is to be assigned; i.e. , nume ri c-cons tan ts shall be supplied as input for numeric- variables, and either quoted-strings or unquoted-strings shall be supplied as input for string-variables. If the response to input for a string-variable is an unquoted-string, leading and trailing spaces shall be ignored (see 4). If the evaluation of a numeric datum causes an underflow, then its value shall be replaced by zero. Subscript expressions in the variable-list are evaluated after values have been assigned to the variables preceding them (i.e. to the left of them) in the variable-list. No assignment of values in the input-reply shall take place until the input-reply has been validated with respect to the type of each datum, the number of input items, and the allowable range for each datum.

15.5 Exceptions

  • The type of datum does not match the type of the variable to which it is to be assigned (nonfatal, the recommended recovery procedure is to request that the input-reply be re-supplied).
  • There is insufficient data in the input-list (nonfatal, the recommended recovery procedure is to request that the input- reply be resupplied).
  • There is too much data in the input-list (nonfatal, the recommended recovery procedure is to request that the input- reply be resupplied).
  • The evaluation of a numeric datum causes an overflow (non- fatal, the recommended recovery procedure is to request that the input-reply be resupplied).
  • A string datum contains too many characters (nonfatal, the recommended recovery procedure is to request that the input- reply he resupplied).

15.6 Remarks

This Standard does not require an implementation to perform any editing of the input-reply, though such editing may be performed by the operating environment. It is recommended that the input-prompt consists of a question- mark followed by a single space. This Standard does not require an implementation to output the input-reply. It is recommended that implementations report an underflow as an exception and allow the input-reply to be resupplied.

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