Files, Continued

Exercises

Exercise 0: Preparation

If you have not done so already, please finish the first lab on files.

Scan through readutils.ss, a collection of utilities for reading from files.

Exercise 1: Averaging a line of values

a. Create a file, values, of at least four lines that contains at least two numbers on each line.

b. Using read-line-of-values, write a procedure that opens values, reads each line, computes an average for that line, and prints out the average.

Exercise 2: Dealing with columnar data

Consider the class list, as distributed by the registrar.

• Columns 1 and 2 are the "number" of the student in the class.
• Column 3 is a period
• Column 4 is a space
• Columns 5 through 30 (I think) are the student's name.
• You can figure out the rest.

a. Write a procedure that reads in the lines of the class list and prints out only the majors. You should use read-line (from our string-library) and substring.

b. Write a procedure that writes a summary of the class year and majors of the students to a file, cs151.summary. Here's some sample (incorrect) contents:

Years:
1st:  20
2nd:   5
3rd:   2
4th:  10

Majors:
UND: 10
GRM:  5
BIO:  1
MAT:  6