Computer programming - Week 4 practice problems

1.Reformat text. Write a program that reads a text until EOF and prints it out transformed with the following three rules:

• any sequence of spaces is replaced by a single space
• any period (dot) is followed by a newline
• there is no whitespace at the start or end of any line

2. Reverse line. Write a recursive function that reads a line of text (until newline or EOF) and prints it with characters in reverse order.
Use the following recursive definition of reversal: reverse(empty) = empty . reverse(cS) = reverse(S)c where c is a char and S is a string.

3. Balanced parantheses. Write a program that reads input until EOF and checks that any parantheses ( ), brackets [ ] or braces { } are properly nested and matched.

4. From infix to postfix. An expression in postfix form is either a natural number, or two expressions followed by an operator + - * / and separated by any whitespace.
Example: 7 4 2 + - 5 - means 7 - (4 + 2) - 5
Adapt the expression calculator done in class to read an expression (in usual infix notation) from input and print it in postfix form.
Instead of returning values, each of the functions will now print. No parantheses are needed or used in postfix form.