demonstrate use of a “for loop” in the design and development of a java program to calculate the...
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Lecture 9.2
Revision of arrays and “for” loops
Demonstrate use of a “for loop” in the design and development of a Java program to calculate the total of a one-dimensional array of 6 integers.
Design your test data (use numbers that will be easy to check for the correct answer):◦ 10, 20, 30, 40, 50, 60◦ Expected total is 210.
Design and code a solution to the problem.
Coding from a design
while (condition) { // if false then loop not executedstatement(s) inside the loop
} // end while
do { // always done at least oncestatement(s) inside the loop
} while (condition) // end do
for (control initial value; (condition) ; control update) {// if false then loop not executed statement(s) inside the loop} // end for
Different types of loop
Condition is always either true or false.
while and do: something must be updated inside the loop which affects the condition (so that it is not an endless loop).
for: something is updated inside the “for” statement which affects the condition (so that it is not an endless loop).
e.g. while (i < 4) { System.out.println("i "= " + i); i = i + 1; } // end while
for (it is raining; while it rains; check if it is raining) {I will need my umbrella} // end for(the for loop has ended therefore the condition must now be false)
// I do not need my umbrella because it is not raining.
The for loop will not be executed if the condition is false, just like the while loop.
For loop example conditionthen clause
Remember the while loop example?while (it is raining) {
then I will need my umbrella} // end while// Now I do not need my umbrella// (because it must have stopped raining)
For loop (poor) example
for (it is raining; while it rains; check if it is raining) {I will need my umbrella
} // end for// (now the condition must be false)// Now I do not need my umbrella because it must not be raining.
For loop formatconditionthen clause
initialisation statement
loop condition
increment statement
Normally we use a for loop when we know how many times we want to execute the loop.
for (i = 0; i < 5; i++) {statement(s)
} // end for
Has the same effect as:
For loop example conditionthen clause
loop control variable is i
initialisation statement i = zero
loop condition while i < 5 is true
int i = 0;while (i<5){ statement(s) i++; // must not forget to update the control variable} // end while
increment statement add 1 to i
if (it is raining) {then I will need my umbrella
for (it is raining; while it is raining; check for rain) { then I will need my umbrella
} // end for} // end ifNow I do not need my umbrella
if (your_age < 65) for (the_age = your age; the_age < 65; the_age++) {
then you cannot get your state pension } // end for} // end ifNow you can get your state pension
for and if example conditionthen clause
initialisation statement
loop condition
increment statement
for (it is raining or snowing; it is raining or snowing; check weather)then I will need my umbrella
} // end while// I will not need my umbrella //(because it is not raining and it is not snowing)
for (it is sunny and hot; it is sunny and hot; check weather) {then I will need a sunshade and a cold drink
} // end while// I will not need a sunshade and a cold drink// (this means it is not both sunny and hot// it might be sunny but cold, or it might be cloudy but hot, // either way I have no sunshade and get no drink)
Complex expression (and/or)
initialisation statement
loop conditionincrement statement
import javax.swing.JOptionPane;public class week9 { public static void main (String[] args) { int i=0; int j=0; for (i = 1; i < 5 && j < 5; i++) {
// statements }
System.out.println("i = " + i + " j = " + j); }}
Complex expression (and)
initialisation statement
loop condition
increment statement
import javax.swing.JOptionPane;public class week9 { public static void main (String[] args) { int i=0; int j=0; for (i = 1; i < 5 || j < 5; i++) {
// statements }
System.out.println("i = " + i + " j = " + j); }}
What would happen if we ran this program?
Complex expression (or)
initialisation statement
loop condition
increment statement
for (i = 1; i < 5; i = i + 1) { statement(s) for (j = 1; j < 5; j = j + 1) {
statement(s)
} // end for
} // end for
Nested for initialisation statement
initialisation statement
loop condition
loop condition
increment statement
increment statement
Demonstrate use of a “for loop” in the design and development of a Java program to calculate the total of a one-dimensional array of 6 integers.
Design your test data (use numbers that will be easy to check for the correct answer):◦ 10, 20, 30, 40, 50, 60◦ Expected total is 210.
Design and code a solution to the problem.
Demonstrate use of “for loop”
Think about the meaning.
How can we use a for loop here?
Normally we use a for loop when we know how many times we want to execute the loop.
We could use a loop to access each element of the array one at a time.
We will need a variable to hold the total, and a variable to count the elements of the array.
1. Get unknown data and create variables.1.1 create an array with values 10, 20, 30, 40, 50, 60.1.2 create and zeroise total.1.3 create and zeroise counter.
2. Processing.2.1 count for six times 2.2 add current array value to total2.3 end for
3. Output.3.1 Output the total.
Algorithm with for
Activity Diagram
22
[count >= 6]
Zeroise total
Total = total + array[count]
[count < 6]
Output total
Array = 10, 20, 30, 40, 50, 60
Zeroise counter
Add 1 to count
//1. Get unknown data and create variables.//1.1 create an array with values 10, 20, 30, 40, 50, 60. //1.2 create and zeroise total.
// 1.3 create and zeroise counter.
//2. Processing.//2.1 count for six times
//2.2 add current array value to total
//2.3 end for
//3. Output.
//3.1 Output the total.
Make algorithm into comments
//1. Get unknown data and create variables.//1.1 create an array with values 10, 20, 30, 40, 50, 60.int [] number = {10, 20, 30, 40, 50, 60}; //1.2 create and zeroise total.int total = 0;// 1.3 create and zeroise counter.int count = 0;
//2. Processing.//2.1 for six times
for (count=0;count<6;count++) {//2.2 add current array value to total
total = total + number[count];//2.3 end for
} // end for//3. Output.
//3.1 Output the total.System.out.println("The total is " + total);
Add the code
Remember in Java the first element of an array is referred to as position zero.