teaching machines

CS 145 Lecture 20 – For Loops

October 17, 2014 by Chris Johnson. Filed under cs145, fall 2014, lectures.

Agenda

• what ?s
• alphabet
• fillDown
• indexOf
• program this

TODO

• Start homework 4, which is due before October 31. This is a full homework. You will want to use the full two weeks.
• Read sections 5.1, 2.3-2.4, and 4.2. Turn in next lecture a 1/4 sheet with questions, observations, and examples of algorithmic repetition you see in life.

Program This 1

• Write a method fillDown that prints a series as shown in the spreadsheet. What do you need for parameters?
• Write a method indexOf that accepts a String parameter and a character to locate. Return the index of the character. What would you do differently to report the index of the last location? What if you wanted to find the first character after a particular starting point?

Program This 2

Code

Alphabet.java

package lecture1017;

public class Alphabet {
  public static void main(String[] args) {
    for (char c = 'a'; c <= 'z'; ++c) {
      System.out.print(c);
    }
  }
}

Spreadsheet.java

package lecture1017;

public class Spreadsheet {
  public static void main(String[] args) {
    fillDown(1, 3, 10);
  }
  
  public static void fillDown(int first,
                              int second,
                              int times) {
    int difference = second - first;
    
    System.out.println(first);
//    System.out.println(second + 0 * difference);
//    System.out.println(second + 1 * difference);
//    System.out.println(second + 2 * difference);
//    System.out.println(second + 3 * difference);
//    System.out.println(second + 4 * difference);

    for (int i = 0; i <= times - 2; ++i) {
      System.out.println(second + difference * i);
    }

  }
}

StringUtilities.java

package lecture1017;

public class StringUtilities {
  public static void main(String[] args) {
    System.out.println(indexOf("Lincoln, Abraham", '!'));
  }
  
  public static int indexOf(String s, char c) {
    for (int i = 0; i < s.length(); ++i) {
      if (s.charAt(i) == c) {
        return i;
      }
    }
    return -1;
  }
}

Grid.java

package lecture1017;

public class Grid {
  public static void main(String[] args) {
    for (int r = 1; r <= 8; ++r) {
      for (int c = 1; c <= 8; ++c) {
        System.out.printf("%3d", c * r);
      }
      System.out.println();
    }

//    for (int c = 1; c <= 8; ++c) {
//      System.out.printf("%3d", c * 2);
//    }
//    System.out.println();
//
//    for (int c = 1; c <= 8; ++c) {
//      System.out.printf("%3d", c * 3);
//    }
//    System.out.println();

  }
}

Haiku