Question

Find and correct the error(s) in each of the following segments of code: a) for ( i = 100, i >= 1, i++ ) System.out.println( i ); b) The following code should print whether integer value is odd or even: switch ( value % 2 ) { case 0: System.out.println( "Even integer" ); case 1: System.out.println( "Odd integer" ); } c) The following code should output the odd integers from 19 to 1: for ( i = 19; i >= 1; i += 2 ) System.out.println( i ); d) The following code should output the even integers from 2 to 100: counter = 2; do { System.out.println( counter ); counter += 2; } While ( counter < 100 );

Short answer

Correct each segment to fix errors: a) use `;` not `,` for loop. b) Add `break` in `switch`. c) Decrement in loop. d) Use lowercase `while`.

Step-by-step solution

Correcting the For Loop Syntax Error

The for loop in segment (a) uses commas instead of semicolons between its parts. The correct format for a for loop should have semicolons separating the initialization, condition, and increment parts. **Correction** Replace the commas with semicolons: ```java for ( i = 100; i >= 1; i++ ) System.out.println( i ); ``` **Explanation** A for loop in Java has the syntax: `for (initialization; condition; increment)`. This loop will never execute properly with commas, hence the semicolon replacement is necessary. Also, if the intention was to count downwards, it should be `i--` instead of `i++`, given the starting condition.

Adding Break Statement to Switch

In segment (b), the switch statement is missing `break` statements after each `case`. This will result in 'fall-through', meaning both "Even integer" and "Odd integer" might be printed. **Correction** Add `break` after each case: ```java switch ( value % 2 ) { case 0: System.out.println( "Even integer" ); break; case 1: System.out.println( "Odd integer" ); break; } ``` **Explanation** Using `break` prevents the execution of the subsequent case when a match is found, which is commonly desired in control flow.

Correcting the Loop Increment for Odd Integers

In segment (c), the code intends to print odd numbers from 19 to 1 but incorrectly increments `i` by 2. **Correction** Instead of incrementing `i`, you should decrement it. Change `i += 2` to `i -= 2`: ```java for ( i = 19; i >= 1; i -= 2 ) System.out.println( i ); ``` **Explanation** To count backward from 19 to 1 by odd numbers, decrease `i` by 2 each iteration.

Correcting the While Loop Condition

In segment (d), the `while` loop condition is written with a capital "W" which is incorrect. Java is case-sensitive and it should be lowercase. **Correction** Change `While` to `while`: ```java do { System.out.println( counter ); counter += 2; } while ( counter <= 100 ); ``` **Explanation** Using lowercase `while` is necessary because it is a Java keyword, and the correct loop condition ensures even numbers up to 100 are printed. Adjust `counter < 100` to `counter <= 100` to include 100 as well.

Key concepts

Syntax Errors

Syntax errors are common mistakes made in programming that prevent the code from running correctly. In the case of Java, syntax errors occur when the rules governing Java coding are violated. To find syntax errors, it is important to look closely at the structure of your code.
For instance, a common syntax error might involve using commas instead of semicolons in a for loop. As seen in the provided example, replacing commas with semicolons is necessary. The correct usage is `for (initialization; condition; increment)`.
The Java compiler is strict about these rules, and minor mistakes can stop your program from compiling altogether. To fix these issues, carefully compare your syntax to standard conventions and make necessary adjustments.

Control Flow

Control flow in programming determines the order in which individual statements, instructions, or function calls are executed. In Java, control flow is primarily managed through control flow statements such as conditional (`if`, `switch`) and looping (`for`, `while`, `do-while`) statements.
Understanding how to correctly use control flow statements is vital to executing your code in a meaningful way. For example, a switch statement lets your program choose between multiple options based on a variable's value. By adding `break` statements after each `case` in a switch, you ensure the program does not execute more than one case. Without these breaks, all subsequent cases after the matched case will execute.

Loop Corrections

Loops are powerful tools in programming that allow you to run a block of code many times. Yet, without correct logic, loops can quickly become erroneous. In Java, loops like `for`, `while`, and `do-while` need specific attention to their initialization, condition, and iteration instructions.
Consider an intended output of odd integers from 19 to 1. A mistake like incrementing instead of decrementing can cause unexpected results. Correctly setting the loop to decrement from 19 to 1 by 2s (`i -= 2`) ensures odd numbers are printed correctly.
Pay attention to loop conditions and increment/decrement steps to ensure correct execution.

Switch Statement

A switch statement can simplify your code when you need to make multiple decisions based on a single variable. In Java, it is a control flow tool that allows a variable to be tested against a list of values, referred to as cases.
Each case in a switch statement contains a code block that will execute if that case is matched. Importantly, using a `break` statement after each block prevents 'fall-through', where multiple cases are executed in sequence.
This syntax helps avoid unexpected behavior in your code logic, ensuring each case executes independently as intended. Always remember to include `break` to keep control flow tidy and predictable.

Debugging Java Code

Debugging is an essential skill in programming used to identify and fix errors. In Java, debugging involves checking your code for various types of errors, including syntax, logical, and runtime errors.
For effective debugging, use techniques like

• Reading error messages carefully, as they often point directly to errors.
• Using print statements to track variable values and program flow.
• Employing development tools or IDEs with debugging capabilities to set breakpoints and step through your code.
• Ensuring slight syntax issues, like case sensitivity as seen in `while` loops, are adjusted to the Java language requirements.

Developing your debugging skills means you'll spend less time searching for errors and more time writing effective, efficient code.