Loops CS140: Introduction to Computing 1 Savitch Chapter 4 Flow of Control: Loops 9/18/13 9/23/13

written in Java Programs (general solution) transform the initial input values (specific problem) to the final output values (specific solution) Solutions are expressed as – Sequence of statements – Branching – Repetition Design before code – Flowcharts – Activity Diagrams – Pseudo Code thus far in CS140 … 2 − Variables − Classes − Objects and references

Chapter 4 Java Loop Statements (4.1) The while statement The do-while statement Nested loops The for statement Programming with loops (4.2) Graphics Supplement (4.3) 3

Conditional Loops: while and do-while SYNTAX: while (condition) loop body SYNTAX: do loop body while (condition) ; 4 SEMANTICS: repeat the loop body while the condition is true Loop Body can be a single statement, or a {statement block} Condition can be a logical expression or a boolean value (variable or constant)

Repetition: while and do-while SYNTAX: while (condition) loop body SYNTAX: do loop body while (condition) ; 5 loop body true false condition loop body true false condition

What is the output? public static final int MAX = 3; int count = 0; while (count < MAX){ System.out.print(count + “, ”); count++; } 1.(none) 2.0, 1, 2, 3, 3.1, 2, 3, 4.0, 1, 2, 5.(don’t know) 6

public static final int MAX = 3; int count = 0; while (count > MAX){ count++; System.out.print(count + “, ”); } What is the output? 1.(none) 2.0, 1, 2, 3, 3.1, 2, 3, 4.0, 1, 2, 5.idk 7

What is the output? public static final int MAX = 3; int count = 0; while (count < MAX){ count++; System.out.print(count + “, ”); } 1.0, 1, 2, 3, 2.1, 2, 3, 3.0, 1, 2, 4.1, 2, 3, 4 5.idk 8

What is the output? public static final int MAX = 3; int count = 0; while (count < MAX) count++; System.out.print(count + “, ”); 1.0, 2.1, 2, 3, 3.1, 4.3, 5.idk 9

What is the output? public static final int MAX = 3; int count = 0; while (count > MAX) count++; System.out.print(count + “, ”); 1.0, 2.1, 2, 3, 3.1, 4.3, 5.idk 10

What is the output? public static final int MAX = 3; int count = 0; while (count < MAX); count++; System.out.print(count + “, ”); 1.0, 2.1, 2, 3, 3.1, 4.3, 5.(none) 6.idk 11

What is the output? public static final int MAX = 3; int count = 0; while (count > MAX); count++; System.out.print(count + “, ”); 1.0, 2.1, 2, 3, 3.1, 4.3, 5.(none) 6.idk 12

What is the output? public static final int MAX = 3; int count = 0; while (count < MAX) System.out.print(count + “, ”); 1.(none) 2.0, 1, 2, 3, 3.1, 2, 3, 4.0, 0, 0, 0, 0, … 5.idk 13

What is the output? public static final int MAX = 3; int count = 0; do { count++; System.out.print(count + “, ”); } while (count < MAX); 1.0, 1, 2, 3, 2.1, 2, 3, 3.0, 1, 2, 4.1, 2, 3, 4 5.idk 14

What is the output? public static final int MAX = 3; int count = 0; do{ System.out.print(count + “, ”); count += 3; } while (count < MAX); 1.(none) 2.0, 3.0, 3, 4.0, 0, 0, 0, 0, … 5.idk 15

What is the output? public static final int MAX = 3; int count = 0; do System.out.print(count + “, ”); while (count > MAX); 1.(none) 2.0, 3.1, 2, 3, 4.0, 0, 0, 0, 0, … 5.idk 16

What is the output? public static final int MAX = 3; int count = 0; do System.out.print(count + “, ”); while (count < MAX); 1.(none) 2.0, 3.1, 2, 3, 4.0, 0, 0, 0, 0, … 5.idk 17

SYNTAX: while (condition) loop body SYNTAX: do loop body while (condition) ; 18 Loop body true false condition Loop body true false condition 1.for loop 2.while loop 3.do-while loop 4.idk

Repetition: for loop SYNTAX: for (initialization; condition; update) loop body 19 SEMANTICS: Execute the initialization (once) repeat the loop body while the condition is true Execute the update statement after each loop

Repetition Conditionally –while –do-while “pre-determined number of times” can know in advance how many times something should be repeated –for loop 20 Q: So why all the examples of while and do-while where there is counting? A: Easiest way to illustrate how those loops work. Q: So why all the examples of while and do-while where there is counting? A: Easiest way to illustrate how those loops work.

Repetition: for loop SYNTAX: for (initialization; condition; update) loop body 21 Loop body true false condition initialization update

Repetition: for loop int max = 6; int i; for ( i = 0; i < max; i++ ) { System.out.print( i ); } 22 int max = 6; int i = 0; while ( i < max ) { System.out.print( i ); i++; }

Repetition: for loop int max = 6; int i; for ( i = 0; i < max; i++ ) { System.out.print( i ); } System.out.print( “last i ” + i ); 23 int max = 6; for ( int i = 0; i < max; i++ ) { System.out.print( i ); } System.out.print( “last i ” + i );

What is the output? public static final int MAX = 3; int count; for(count = 0; count < MAX; count++) System.out.print(count + “, ”); 1.(none) 2.0, 1, 2, 3.1, 2, 3, 4.0, 0, 0, 0, 0, … 5.idk 24 Print count true false count < MAX count = 0 count++

What is the output? public static final int MAX = 3; int count; for(count = 0; count < MAX; count++); System.out.print(count + “, ”); 1.(none) 2.0, 1, 2, 3.1, 2, 3, idk 25

What is the output? public static final int MAX = 3; int count; for(count = 0; count < MAX; count++) System.out.print(count + “, ”); System.out.print(count); 1. (none)2. 1, 1 2, 2 3, , 1, 2, 34. 1, 2, 3, , 0, 0, 0, 0, … 6. idk 26

What is the output? public static final int MAX = 3; int count; for(count = 0; count < MAX; count+=2) System.out.print(count + “, ”); System.out.print(count); 1. (none)2. 2, , 1, 2, 34. 0, 2, , 2 6. idk 27

What is the output? public static final int MAX = 3; int count; for(count = MAX; count > 0; count--) System.out.print(count + “, ”); System.out.print(count); 1. (none)2. 3, 2, 1, 3. 3, 2, 1, 0,4. 2, 1, 0, 5. 3, 3, 3, 3, 3, … 6. idk 28

What is the output? public static final int MAX = 3; int count; for(count = MAX; count < 0; count--) System.out.print(count + “, ”); System.out.print(count); 1. (none)2. 3, 2, 1, 3. 3, 2, 1, 0, idk 29

Nested loops Loops can be nested just like branching expressions int a = 3; int b = 2; for (int i = 0; i < b; i++) { for (int j = 0; j < a; j++) { System.out.print( j + i ); } System.out.println( i ); } 30

What is the output? public static final int MAX = 3; for (int f1 = 0; f1 < MAX; f1++){ for (int f2 = 0; f2 < MAX; f2++){ System.out.print(f1 + “ + ” + f2); System.out.println(“ = ” + (f1+f2)); } 31 not multi-choice

What is the output? public static final int MAX = 3; int count = 0; while (count < MAX){ for (int f2 = 0; f2 < MAX; f2++){ System.out.print(count + “ ”); } count++; } 32 not multi-choice

What is the output? public static final int MAX = 3; int count = 0; while (count < MAX){ for (int f2 = 0; f2 < MAX; f2++){ System.out.print(f2 + “ ”); } count++; } 33 not multi-choice

Which Loop? Do you know (for any input) how many times the loop body will be executed? Should the loop body execute one or more times? 34

Which Loop? Write a program to read a list of integers and to display the largest, smallest, and average of all integers. The user indicates the end of the input list by entering 0 (zero) while() 2.do-while() 3.for() 4.idk

Which Loop? Write a program to read a list of 20 integers and to display the largest, smallest, and average of all integers while() 2.do-while() 3.for() 4.idk

Which Loop? Write a program that reads a bank account balance and an interest rate and displays the balance of the account in ten years while() 2.do-while() 3.for() 4.idk

Which Loop? Write a program that reads a bank account balance and an interest rate and displays the balance of the account after a number of years entered by the user while() 2.do-while() 3.for() 4.idk

Which Loop? Write a program that reads a bank account balance and an interest rate and displays the balance of the account in ten years. The interest is added each month of each of the ten years while() 2.do-while() 3.for() 4.idk

Which Loop? Write a program that reads a bank account balance and an interest rate and displays the balance of the account in ten years. The interest is added each day of each month of each of the ten years while() 2.do-while() 3.for() 4.idk

Which Loop? Write a program that simulates the falling and bouncing of a ball by computing its height at each 1/10 of a second (of a simulated clock). The user enters an initial height (above the ground) and the program continues until the fifth bounce while() 2.do-while() 3.for() 4.idk

break; and continue; break; - ends only the innermost loop or switch continue; - ends current iteration and proceeds to the next one Only use these if you have a good reason Try to rewrite your code to avoid these 42

Review Three loop statements – Two are top-tested: execute loop body 0+ – One is bottom tested: execute loop body 1+ Loop body can be – a single statement or {statement block} – Branching – Loops Condition can be boolean or logical expression Choose for when number of loops is ‘known’ 43