⎕FI Convert formatted input

The monadic system function ⎕FI is used in conjunction with ⎕VI 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, ⎕VI returns a 1 if the sub-string represents a valid number, and 0 if it does not. ⎕FI 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:

      ⎕FI '100.32 $4 2,,3 0 12.2 ¯3 +2 -2'
100.32 0 0 0 12.2 ¯3 0 0
      ⎕VI '100.32 $4 2,,3 0 12.2 ¯3 +2 -2'
1 0 0 1 1 1 0 0

⎕VI and ⎕FI 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 ⎕SS to translate minus to high-minus first. To allow comma-delimited input, use ⎕SS to translate comma to space:

      STRING←'3,-2,45.5,-0.08'
      ⎕VI STRING
0      
      ⎕SS (STRING; ('-';','); ('¯';' '))
3 ¯2 45.5 ¯0.08
      ⎕VI ⎕SS (STRING; ('-';','); ('¯';' '))
1 1 1 1
      ⎕FI ⎕SS (STRING; ('-';','); ('¯';' '))
3 ¯2 45.5 ¯0.08