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Module 5 Control Structures Loop Statement

2026-03-17 14:22

Tags: #java

Author: Duke Hsu

Key Concepts

  • Looping Statements

    • A looping statements is a control structure that allows a block of code to be executed repeatedly as long as a condition is true, or until a certain limit is reached.
    • Loops are useful when :
      • Displaying numbers in sequence
      • Computing totals
      • Processing multiple records
      • Repeating menu options
      • Iterating through arrays
      • Applying operations to multiple objects

  • Three types of Loop Statement

    • forloop statement
    • while loop statement
    • do while loop statement

do while Loop Statement

Use a do while loop when: - the program must run once before checking. - repeating menu choices. - prompting a user until valid input is given.

The do/while ==loop is a variant of the ==while loop. This loop will execute the code block once, before checking if the condition is true. Then it will repeat the loop as long as the condition is true.

Note

The semicolon ; after the while condition is required!

Syntax: 

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do{
    //code block 
d
}while(condition); //don't forget ';'

Example:

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int = 0;

do{

    System.out.println(i);
    i++; //increasement
}while(i<5); //output 0,1,2,3,4

while Loop Statement

  • The while loop is used when the number of repetitions is not exactly know in advance. It continues as long as the condition remains true.
  • repetition depends on a condition
  • the number of repetitions is uncertain
  • input validation or menu repetition is needed.

Syntax:

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while(condition){

    //code block 

}

Example:

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int countdown = 10;

while(countdown > 0){
    System.out.println(countdown);
    countdown--;
}

//when countdown < 0 , condition is false , then exit the while loop 
System.out.println("Happy New Year!!!");

for Loop Statement

  • The for loop is commonly used when the number of repetitions is already known.

  • Initialization - sets the starting value i = 0;

  • Condition - checked before every repetition i<=5;
  • Update - changes the loop variable after each cycle(loop)i++ or i--

In for loop, initialization only run once , next loop is starts condition , if condition true, execute the code block . then update( increasement or decreasing ) the loop variable

Syntax:

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for (initialization; condition; update){

    //code block

}

Example:

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for (int seat = 1; seat <=5; seat++){

    System.out.println("Seat number: " + seat);
}

References

Module 5 - Control Structure - Loop statement.pptx