## ŒVI Verify formatted input

The monadic system function ŒVI is used in conjunction with ŒFI to validate a text string and convert it to numeric form. In both cases, the argument is a character vector (or scalar), containing one or more sub-strings of characters separated by blanks. For each non-blank sub-string, ŒVI returns a 1 if the sub-string represents a valid number, and 0 if it does not. ŒFI returns the numeric representation of the sub-string, or 0 if it is not a valid number. Numbers are validated and converted in the same way as normal APL input. Scientific notation is supported, and negative numbers are prefixed by the high minus (¯) character. For example:

          ŒFI '100.32 $4 2,,3 0 12.2 ¯3 +2 -2'
    100.32 0 0 0 12.2 ¯3 0 0
          ŒVI '100.32 $4 2,,3 0 12.2 ¯3 +2 -2'
    1 0 0 1 1 1 0 0

ŒVI and ŒFI are usually used to validate and convert user input, or to convert text files to numeric form. To allow users to enter negative numbers using the ordinary (non-APL) minus sign, you can use ŒSS to translate minus to high-minus first. To allow comma-delimited input, use ŒSS to translate comma to space:

          STRING„'3,-2,45.5,-0.08'
          ŒVI STRING
    0
          ŒSS (STRING; ('-';','); ('¯';' '))
    3 ¯2 45.5 ¯0.08
          ŒVI ŒSS (STRING; ('-';','); ('¯';' '))
    1 1 1 1
          ŒFI ŒSS (STRING; ('-';','); ('¯';' '))
    3 ¯2 45.5 ¯0.08

Topic: APLX Help : Help on APL language : System Functions & Variables : ŒVI Verify formatted input

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