Introduction to Computers and Programming Lecture 10: For Loops Professor: Evan Korth New York University

review What are the three parts of every loop? Where are these three parts in a for loop? Where are these three parts in a while loop? Which two parts of the for loop will always be executed? True or False: You must know at compile time how many iterations you want to execute when using a for loop?

Road map Nested for loops break continue Reading: –Liang 5: Chapter 3: 3.3.4; 3.5; 3.6 –Liang 6: Chapter 4: 4.6; 4.9 –Liang 7: Chapter 4: 4.6; 4.9

Nested For Loops It is also possible to place a for loop inside another for loop. int rows, columns; for (rows = 1; rows <= 5; rows++) { for (columns=1; columns<=10; columns++) System.out.print ("*"); System.out.println (); } Outer Loop Inner Loop Output:**************************************************

Nested For Loops, Example #2 int rows, columns; for (rows=1; rows<=5; rows++) { for (columns=1; columns<=rows; columns++) System.out.print ("*"); System.out.println (); } Output:*************** Outer Loop Inner Loop

break and continue

break; We have seen the keyword break used in a switch statement: switch (userInput) { case 1: userInput++; break; } You can also use break inside of a for, while or do/while loop to immediately exit from the loop.

Example of break use public class Break { public static void main (String [] args) { int x; for ( x = 1 ; x <= 10; x++) { if (x == 5) break; System.out.println("The number is : " + x); } /* end for x = 1... */ }

continue Continue is a statement which can be used inside a for, while or do/while loop in order to skip the rest of the remaining code in the loop, and start the next iteration.

Example of continue public class Continue { public static void main (String [] args) { int x; for ( x = 1 ; x <= 10; x++) { if (x == 5) continue ; System.out.println("The number is : " + x); } /* end for x = 1... */ }

Java Keywords  2003 Prentice Hall, Inc. All rights reserved.

Problem Use a while loop with a sentinel to read in letter grades of the form A, B, C, D, F. Convert the grades to numerical equivalents, based on the following table, then print out the average grade in numerical form Num FDCBALetter

Structured Programming: Summary

Summary Sequence –Statement follow one another Selection Structures –if –if/else –if/else if/else –switch Repetition Structures –while –do/while –for

midterm Tuesday, March 10 th during class You will have the entire class period to complete the exam 5short answer(total of 15 points) 1find the errors(15 points) 1 || 2medium answer(20 points) 2write a program(total of 50 points) –Remember the difference between write the program and write the main method.

Midterm material From the book: –All the sections listed in each of the slide presentations. –Reading the case studies in the chapters is a good idea even though we did not cover all of them in class. That does not mean I will ask you to write one of those programs. The practice is good –I also suggest you practice problems from the end of each chapter. Anything in the class notes. Next class: Thursday, March 5 will be a review session where we practice exam-like questions.