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212 10 Transforming with Traditional Programming Languages

1/15/2000 18.66 normal 62 cm 46.27 kg 102 lb

1/15/2000 26.93 overweight 63 cm 68.95 kg 152 lb

2/1/2000 33.95 obese 65 cm 92.53 kg 204 lb

2/1/2000 17.38 normal 67 cm 50.35 kg 111 lb

The first step is to remove any extra space at the beginning and end of the

line. This is done with thechompfunction. This was not necessary in previ-

ous programs because the fields were in fixed locations in the line. It is a good

idea to usechompwhenever the input has variable-length fields. The next

step is to split the record into fields using thesplitoperator. This produces

the@recordarray. The values in this array are denoted by$record[0],

$record[1], $record[2],...The number in brackets is called thein-

dexorpositionof the value in the array. If one uses a negative index, then it

specifies a position starting from the last value (i.e., starting from the other

end of the array). Notice that the array as a whole uses@but the individual

values use$. Remember that in Perl, the initial character on a variable (and

there are more than just$and@) denotes the kind of value. It is not part of

the name of the variable.

The next step is to split the first field (i.e., the date) into its parts. The parts

are separated by slashes. The rest of the program is the same as the first

program except that array values are used instead of substrings. Another

difference is that the conditional statements are written with the if-conditions

first rather than after the statement. The first condition is indicated byif.

Subsequent conditions (except the last one) are indicated usingelsifwhich

is short for “else if”. The last case is indicated byelsewhich is used for

those cases not handled any other case. Putting the conditional after the

statement as in the first program is best if you think of the statement as being

subject to a condition. Putting a conditional before the statement is best if

you are thinking in terms of a series of cases, such that only one of them

applies to each record.

The split statement

@record = split(" ", $_);

could have been abbreviated to

@record = split(" ");

The default for splitting is to split up the value of$_. One can even abbrevi-

ate further to