CS173: Intro to Computer Science - Iteration over Strings

Activity Goals

The goals of this activity are:
  1. To be able to apply iteration and conditionals to a String

Supplemental Reading

Feel free to visit these resources for supplemental background reading material.

The Activity

Directions

Consider the activity models and answer the questions provided. First reflect on these questions on your own briefly, before discussing and comparing your thoughts with your group. Appoint one member of your group to discuss your findings with the class, and the rest of the group should help that member prepare their response. Answer each question individually from the activity, and compare with your group to prepare for our whole-class discussion. After class, think about the questions in the reflective prompt and respond to those individually in your notebook. Report out on areas of disagreement or items for which you and your group identified alternative approaches. Write down and report out questions you encountered along the way for group discussion.

Model 1: Looping over Each Character

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public class Main {
    public static void main(String[] args) {              
        String str = "Hello!";
         
        for(int i = 0; i < str.length(); i++) {
            System.out.println("Give me a " + str.charAt(i));
        }
    }
}

Questions

  1. What is the value of str.length()?
  2. Why does this loop not start at the initial value 1?

Model 2: Iterative Algorithms Using the String

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public class Main {
    public static void main(String[] args) {
        String x = "test";
         
        boolean containsT = false;
        int numT = 0;
         
        for(int i = 0; i < x.length(); i++) {
            if(x.charAt(i) == 't') {
                containsT = true;
                numT++;
            }
        }
    }
}

Questions

  1. For what values of i will the character ‘t’ be found in this String? You may find the Java Visualizer or your IDE debugger helpful.
  2. Write a function that accepts a String x, a char c, and an int n. Return the index of the n’th instance of the character c in the String x. Use the indexOf() method in a loop.

Embedded Code Environment

You can try out some code examples in this embedded development environment! To share this with someone else, first have one member of your group make a small change to the file, then click "Open in Repl.it". Log into your Repl.it account (or create one if needed), and click the "Share" button at the top right. Note that some embedded Repl.it projects have multiple source files; you can see those by clicking the file icon on the left navigation bar of the embedded code frame. Share the link that opens up with your group members. Remember only to do this for partner/group activities!

Submission

I encourage you to submit your answers to the questions (and ask your own questions!) using the Class Activity Questions discussion board. You may also respond to questions or comments made by others, or ask follow-up questions there. Answer any reflective prompt questions in the Reflective Journal section of your OneNote Classroom personal section. You can find the link to the class notebook on the syllabus.

For Additional Practice

Feel free to visit these resources for additional practice exercises.