Homework: Text Files

Problem 1. Odd lines

• Write a program that reads a text file and prints on the console its odd lines.

Problem 2. Concatenate text files

• Write a program that concatenates two text files into another text file.

Problem 3. Line numbers

• Write a program that reads a text file and inserts line numbers in front of each of its lines.
• The result should be written to another text file.

Problem 4. Compare text files

• Write a program that compares two text files line by line and prints the number of lines that are the same and the number of lines that are different.
• Assume the files have equal number of lines.

Problem 5. Maximal area sum

• Write a program that reads a text file containing a square matrix of numbers.
• Find an area of size 2 x 2 in the matrix, with a maximal sum of its elements.
  • The first line in the input file contains the size of matrix N.
  • Each of the next N lines contain N numbers separated by space.
  • The output should be a single number in a separate text file.

Example:

input	output
4 2 3 3 4 0 2 3 4 3 7 1 2 4 3 3 2	17

Problem 6. Save sorted names

• Write a program that reads a text file containing a list of strings, sorts them and saves them to another text file.

Example:

input.txt	output.txt
Ivan Peter Maria George	George Ivan Maria Peter

Problem 7. Replace sub-string

• Write a program that replaces all occurrences of the sub-string start with the sub-string finish in a text file.
• Ensure it will work with large files (e.g. 100 MB).

Problem 8. Replace whole word

• Modify the solution of the previous problem to replace only whole words (not strings).

Problem 9. Delete odd lines

• Write a program that deletes from given text file all odd lines.
• The result should be in the same file.

Problem 10. Extract text from XML

• Write a program that extracts from given XML file all the text without the tags.

Example:

<?xml version="1.0"><student><name>Pesho</name><age>21</age><interests count="3"><interest>Games</interest><interest>C#</interest><interest>Java</interest></interests></student>

Problem 11. Prefix "test"

• Write a program that deletes from a text file all words that start with the prefix test.
• Words contain only the symbols 0…9, a…z, A…Z, _.

Problem 12. Remove words

• Write a program that removes from a text file all words listed in given another text file.
• Handle all possible exceptions in your methods.

Problem 13. Count words

• Write a program that reads a list of words from the file words.txt and finds how many times each of the words is contained in another file test.txt.
• The result should be written in the file result.txt and the words should be sorted by the number of their occurrences in descending order.
• Handle all possible exceptions in your methods.