4.11 Exercises

Exercise 4.1

Explore the sensitivity of programming languages to errors of syntax. Try removing the semicolon from the end of any statement of one of our working programs and examining the error messages that result, if any. Try changing other syntactical items: add a parenthesis or a curly brace; misspell "print" or some other reserved word; just type in, or delete, anything. Programmers get used to seeing such errors; even after getting to know the language well, it is still common to have some syntax errors as you gradually add code to a program. Notice how one error can lead to many lines of error reporting. Is Perl accurately reporting the line where the error is?

Exercise 4.2

Write a program that stores an integer in a variable and then prints it out.

Exercise 4.3

Write a program that prints DNA (which could be in upper- or lowercase originally) in lowercase (acgt); write another that prints the DNA in uppercase (ACGT). Use the function tr///.

Exercise 4.4

Do the same thing as Exercise 4.3, but use the string directives \U and \L for upper- and lowercase. For instance, print "\U$DNA" prints the data in $DNA in uppercase.

Exercise 4.5

Sometimes information flows from RNA to DNA. Write a program to reverse transcribe RNA to DNA.

Exercise 4.6

Read two files of data, and print the contents of the first followed by the contents of the second.

Exercise 4.7

This is a more difficult exercise. Write a program to read a file, and then print its lines in reverse order, the last line first. Or you may want to look up the functions push, pop, shift, and unshift, and choose one or more of them to accomplish this exercise. You may want to look ahead to Chapter 5 so you can use a loop in this program, but this may not be necessary depending on the approach you take. Or, you may want to use reverse on an array of lines.