CS 1: Lecture 21 – Loops, Part 3
October 27, 2017 by Chris Johnson. Filed under
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cs1, cs145, cs148, fall 2017, lectures.
Dear students,
We explore more examples of loops today. Because we are, in fact, stuck in a loop. There’s no way out of this.
- Write a program that prompts a user for a file. Report how many bytes it occupies on disk. If a bad file is entered, repeat the prompt until the user gets it right. Follow this general repeat until valid pattern:
prompt
x = get user input
while x is not valid
prompt
x = get user input
// if we get here, the input must be valid
process x
- Write a method that accepts an
int and returns the number of factors that evenly divide that number. Do not count 1 or the number itself. Use that method to find the number in [0, 1000] that has the most factors.
- Write code that generates all possible two-byte Unicode characters. There are 65536 of them.
- Write a program that generates a random spelunking workout display. For example:
**********
*******
*********
****
******
*******
- Write a program that presents a text-based spinner that cycles through
-, /, |, and \. Print each new “frame” of the animation over the previous frame. Use a carriage return (\r) in your output to force the cursor back to the left margin.
Here’s your TODO list to complete before we meet again:
- The homework 4 SpecChecker has been posted. Run Team / Pull… from template today to bring it into your repository. Solving configuration issues is part of completing a homework.
See you next class!
Sincerely,
P.S. It’s time for a haiku!
Sorry I’m so late
My self-driving car got stuck
In a roundabout
P.P.S. Here’s the code we wrote together in class…
Spacer.java
package lecture1027;
import java.io.File;
import java.util.Scanner;
public class Spacer {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int nFailures = 0;
File file;
do {
System.out.print("Enter a filename: ");
String name = in.nextLine();
file = new File(name);
if (!file.exists()) {
++nFailures;
}
} while (!file.exists() && nFailures < 3);
System.out.println(nFailures);
if (nFailures == 3) {
System.err.println("You shall not pass.");
} else {
System.out.println(file.length() / 1024.0 / 1024);
}
}
}
Spelunking.java
package lecture1027;
import java.util.Random;
public class Spelunking {
public static void main(String[] args) {
Random g = new Random();
int n = g.nextInt(100);
for (int i = 0; i < n; ++i) {
System.out.println(getRandomLine(g));
}
}
public static String getRandomLine(Random g) {
int n = g.nextInt(15) + 1;
String line = "";
for (int i = 0; i < n; ++i) {
line += "*";
}
return line;
}
}
Unicode.java
package lecture1027;
public class Unicode {
public static void main(String[] args) {
for (int i = 0; i < 65536; ++i) {
System.out.print((char) i);
if (i % 20 == 0) {
System.out.println();
}
}
}
}
Factor.java
package lecture1027;
public class Factor {
public static void main(String[] args) {
int max = 0;
int winnerSoFar = 0;
for (int i = 1; i <= 1000; ++i) {
int count = factorCount(i);
// max = Math.max(count, max);
if (count > max) {
System.out.println(i + " -> " + count);
max = count;
winnerSoFar = i;
}
}
System.out.println(winnerSoFar);
}
public static int factorCount(int n) {
int nFactors = 0;
for (int i = 2; i < n; i++) {
if (n % i == 0) {
nFactors += 1;
}
}
return nFactors;
}
}