Introduction to While and For Loops in Java

1. Week 8 Introduction to Computer Science and Object-Oriented Programming COMP 111 George Basham

2. Week 8 Topics 8.1.1 while Loops 8.1.2 for Loops

3. 8.1.1 while Loops • It is often useful to be able to repeatedly execute one or more statements • A loop refers to such a repetition • A while loop statement executes a block of code repeatedly. A condition controls how often the loop is executed.

4. 8.1.1 while Loops cont. • The while loop statement construct is while (condition) statement; • Use brackets if there are multiple statements in the body of the while loop statement • while (balance < targetBalance) { years++; double interest = balance * rate / 100; balance = balance + interest; }

5. 8.1.1 while Loops cont. False balance < targetBalance ? True Increment years Add interest to balance

6. 8.1.1 while Loops cont. • The do/while loop can be used if the loop should always be executed at least one time • The do/while loop statement construct is do statement; while (condition) double value; do { System.out.print(“Enter a positive number: ”; value = in.nextDouble(); } while(value <= 0);

7. 8.1.2 for Loops • The for loop is useful when the number of iterations are known • The for loop statement construct is for (initialization; condition; update) statement; • for (i = 1; i <= years; i++) { double interest = balance * rate / 100; balance = balance + interest; }

8. 8.1.2 for Loops cont. i = 1 initialization False condition i <= years? True Add interest to balance update i++

9. 8.1.1 and 8.1.2 Loops cont. • Review the textbook (sections 7.1 and 7.2) to learn to avoid these loop coding pitfalls: • Infinite loops • Off-by-One errors • Spaghetti code • Use for loops for their intended purpose • Forgetting a semicolon • A semicolon too many • Don’t use != to test the end of a range

10. Reference: Big Java 2nd Edition by Cay Horstmann 8.1.1 while Loops (section 7.1 in Big Java) 8.1.2 for Loops (section 7.2 in Big Java)