479: Mainline

As you learned in Segment 462, you denote a particular character by prefixing that character with a $ prefix, thus distinguishing the character from, say, a variable name. For example, you denote the character V by writing $V.

If you want to see whether you have extracted a particular character, you compare what you have extracted with that character. Then, if you wish, you can build an ifTrue: expression on that comparison, as in the following example, which prints only those strings for which the first character is V:

Food method definition • class 
eatOnlyVegetables: aFile 
  |inputStream string | 
  inputStream := File pathName: aFile. 
  [inputStream atEnd] 
    whileFalse: 
      [(string := inputStream nextLine) notEmpty 
       ifTrue: [(string at: 1) = $V 
                  ifTrue: [Transcript show: string printString; cr]]]. 
  inputStream close 
Workspace
Food eatOnlyVegetables: 'c:\test\foods.dta' 
Transcript 
'V Broccoli  3  16   9   0.5c            ' 
'V Carrots   1  33   4   0.5c            good for rabbits' 
'V Corn      1  23   6   0.5c' 
'V Cabbage   2  14   3   0.5c'