Example 1: Sum the numbers from 1 to 10
Suppose we want to calculate the sum of the numbers from 1 to 10. We could do the
following:
sum = 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10;
or we could recognize that this is really the set of steps:
1. sum = 1
2. sum = sum + 2
3. sum = sum + 3
4. sum = sum + 4
5. sum = sum + 5
6. sum = sum + 6
7. sum = sum + 7
8. sum = sum + 8
9. sum = sum + 9
10. sum = sum + 10
So to write our program we will need:
1. A variable that will be used to accumulate our sum, called “sum”.
2. A variable that will represent the set of numbers that will be added to
sum.. (1, 2, 3, 4, 5…) which we will call “x”.
3. Both should be integers.
4. Our loop will exit when x is greater than 10. We will loop while x < = 10
public class Sumto10 {
public static void main (String args[]) {
int sum, x;
sum = 0;
x = 1;
This prints:
while ( x <= 10) {
sum = sum + x;
x = x + 1;
}
The sum of the numbers from 1 to 10 is: 55
System.out.println(“The sum of the numbers from 1 to 10 is: “ + sum);
}
}
Example 2: What if we needed to do a more generalized type of calculation? Instead of
just the numbers from 1 to 10, but sum the numbers from 1 to N where N is a number
input by the user…
The steps are the same: sum = sum + 1, sum = sum + 2….. sum = sum + n
We would do the following alterations to our program:
1. We would create a new variable “n”, and prompt the user to input an integer value
for n.
2. We would loop as long as x < = n
--------------------------------------------------------------------------------------------------public class Sumton {
public static void main (String args[]) {
int sum, x, n;
System.out.println(“Please enter an integer number, N, and we will calculate the “
+ “ sum from 1 to N “);
n = (int) ReadItem.getLong();
sum = 0;
x = 1;
while ( x <= n) {
sum = sum + x;
x = x + 1;
}
System.out.println(“The sum of the numbers from 1 to “ + n + “ is: “ + sum);
}
}
/home/hayhurst/java- java Sumton
Please enter an integer number, N, and we will calculate the sum from 1 to N
20
PRE-TEST LOOPS:
The sum of the numbers from 1 to 20 is: 210
Example 3: As another example, lets take the calculator program we created in a
previous class using a switch statement, and modify it so that it can allow the user to
enter multiple calculations. Originally it was implemented as:
import java.util.*;
public class switchEx2 {
public static void main(String args[])
{
Scanner in = new Scanner(System.in);
int a,b;
char ch;
String input;
System.out.println ("Do you want to Add, Subtract, Multiply or " +
"Divide?");
System.out.print ("Please enter the first letter of what you would"
+ " like to do?");
ch= (in.next().toUpperCase()).charAt(0);
System.out.println ("Enter first number: ");
a = in.nextInt();
System.out.println ("Enter second number: ");
b = in.nextInt();
switch (ch)
{
case 'A':
System.out.println ("Answer is "+ (a+b));
break;
case 'S':
System.out.println ("Answer is "+ (a-b));
break;
case 'M':
System.out.println ("Answer is "+ (a*b));
break;
case 'D':
if (b != 0) System.out.println ("Answer is "+ (a/b));
else System.out.println("Division by zero");
break;
default :
System.out.println("Invalid Operation");
} //end of switch
System.out.println("Good bye");
}
}
As originally implemented it only allowed to user to enter a single calculation, to change
to multiple our program will need to be able to :




Input the desired operation multiple times
Input 2 integers for each operation
Determine the operation entered and perform the calculation for each
operation and print the result.
We will need to allow the user to enter something special to indicate when
they are finished performing calculations…. Perhaps “Q”
The steps of our program will look like:
1. Prompt for and get the first operation from the user.
2. If the operation entered is “q”, exit the program and do nothing.
3. If the operation is not q, then enter the loop,
a. Prompt for the 2 integers to be used in the calculation
b. Identify the operation entered, and perform the calculation
c. Print the results
d. Prompt for and get the NEXT operation.
e. Return to step 2
---------------------------------------------------------------------------------------------------------
import java.util.*;
public class switchEx2 {
public static void main(String args[])
{
Scanner in = new Scanner(System.in);
int a,b;
char ch;
String input;
System.out.println ("Do you want to Add, Subtract, Multiply or Divide?");
System.out.print ("Please enter the first letter of what you would like to do or Q to quit");
1
ch= (in.next().toUpperCase()).charAt(0); // read the input
while ( ch != ‘Q’) {
System.out.println ("Enter first number: ");
a = in.nextInt();
System.out.println ("Enter second number: ");
b = in.nextInt();
2
3
switch (ch)
{
case 'A':
System.out.println ("Answer is "+ (a+b));
break;
case 'S':
System.out.println ("Answer is "+ (a-b));
break;
case 'M':
System.out.println ("Answer is "+ (a*b));
break;
case 'D':
if (b != 0) System.out.println ("Answer is "+ (a/b));
else System.out.println("Division by zero");
break;
default :
System.out.println("Invalid Operation");
} //end of switch
5
System.out.println ("Do you want to Add, Subtract, Multiply or Divide?");
System.out.print ("Please enter the first letter of what you would like to do or Q to quit");
ch= (in.next().toUpperCase()).charAt(0); // read the input
} // end of the loop body
System.out.println("Good bye");
}
}
1.
2.
3.
4.
5.
4
Get the initial operation to perform
Loop while the operation is not quit
Get the numbers used in the calculation
Perform the calculation
Get the next operation and return to the top of the loop
Example 4: Sum the numbers from 1 to 10.
public class Sumto10 {
public static void main (String args[]) {
int sum, x;
sum = 0;
x = 1;
do {
sum = sum + x;
x = x + 1;
} while (x <= 10);
System.out.println("The sum of the numbers from 1 to 10 is: " + sum);
}
}
/home/hayhurst/java- java Sumto10
The sum of the numbers from 1 to 10 is: 55
Example 5:
public class Sumto10 {
public static void main (String args[]) {
int sum, x;
sum = 0;
x = 20;
do {
sum = sum + x;
x = x + 1;
} while (x <= 10);
System.out.println("The sum of the numbers from 1 to 10 is: " + sum);
}
}
/home/hayhurst/java- java Sumto10
The sum of the numbers from 1 to 10 is: 20
Example #6: For loops
Sum the numbers from 1 to n.
public class Sumto10for {
public static void main (String args[]) {
int sum, x;
sum = 0;
for ( x = 1 ; x <= 10 ; x ++)
sum = sum + x;
System.out.println("The sum of the numbers from 1 to 10 is: " + sum);
}
}
/home/hayhurst/java- java Sumto10for
The sum of the numbers from 1 to 10 is: 55
Example #7
public class Sumto10for {
public static void main (String args[]) {
int sum, x=1;
sum = 0;
for (; x <= 10 ; x ++)
sum = sum + x;
System.out.println("The sum of the numbers from 1 to 10 is: " + sum);
}
}
Example #8
public class Sumto10for {
public static void main (String args[]) {
int sum, x=1;
sum = 0;
for (sum = 0, x = 1; x <= 10 ; x ++)
sum = sum + x;
System.out.println("The sum of the numbers from 1 to 10 is: " + sum);
}
}
Example 8b:
public class Sumto10fora {
public static void main (String args[]) {
int sum, x=1;
sum = 0;
for ( ; ; ) {
sum = sum + x;
x++;
if (x > 10) break;
}
System.out.println("The sum of the numbers from 1 to 10 is: " + sum);
}
}
Example #9:
public class Sumto10for {
public static void main (String args[]) {
int sum;
sum = 0;
for (int x = 1; x <= 10 ; x ++)
sum = sum + x;
System.out.println("The sum of the numbers from 1 to 10 is: " + sum);
}
}
NOTE: IF YOU DECLARE THE LOOP CONTROL VARIABLE IN THE LOOP
INITIALIZATION SECTION, YOU CAN ONLY HAVE ONE STATEMENT IN THAT
SECTION!!!
Example 10
public class IsPrime {
public static void main (String args[]) {
int inputValue, i;
System.out.println(“Please enter a positive Integer. “ );
inputValue = (int) ReadItem.getLong();
if ((inputValue == 2) || ( (inputValue % 2) == 0 )
System.out.println( inputValue + “is a Prime Number”);
else {
for (i = 3; i < inputValue; i += 2) {
if ((inputValue % i) == 0) {
System.out.println( inputValue + “is NOT a Prime Number”);
break;
} // end of if
} // end of for loop
if ( i == inputValue)
System.out.println( inputValue + “is a Prime Number”);
} // end else
} }