Java Notes 5 – Control Statements
If, While, For

5.1 If Statement

The if statement allows your program to make a decision.  The following operators may be used:
<   >   <=   >=   ==   !=   ||   &&   !

If Statement Examples

int A = 5;
if (A > 3)
   System.out.println("A is greater than 3");

 A is greater than 3
double Salary = 12.75;
if (Salary > 15.0)
   System.out.println("You are well paid");
else
   System.out.println("You should work harder");		 You should work harder 
// Braces are needed when multiple statements follow
// an if statement

float HoursWorked = 45.0;
float Wage = 10.0
if (HoursWorked > 40.0)
{
   System.out.println("You worked overtime");
   Wage = Wage * 1.5;
}		  You worked overtime
// OR operator ||

float Wage = 8.85;
if (Wage < 10.0 || Wage > 20.0
   System.out.println("You make too little or too much");

 You make too little or too much
// AND operator &&

float Wage = 12.75;
if (Wage >= 10.0 && Wage <= 20.0
   System.out.println("You have a good wage");

 You have a good wage
// Nested if statement
int Age = 25;
if (Age < 10)
   System.out.println("You are less than 10");
else if (Age < 20)
    System.out.println("You are over 10 but less than 20");
else if (Age < 30)
    System.out.println("You are over 20 but less than 30");
else
   System.out.println("You are over 30");		 You are over 20 but less than 30

5.2 While Loop

The while loop will execute a body of statements continuously as long as the condition is true.

While Loop Examples

int X = 1;
while (X <= 5)
{
   System.out.print("Yes");
   X++;
}

  YesYesYesYesYes
// Continuously displays dialog unto "No" selected

int Continue = 0;
while (Continue <= 0)
{
   Continue = JOptionPane.showConfirmDialog(null,
      "Continue Looping","Continue",0,3);
}		     

5.3 For Loop

A for loop is useful when a set number of iterations is known.  After the for statement, there are three sections in the parenthesis:
1. Initialize the control variable - executes once at the beginning of the loop
2. Condition - test if true before each iteration
3. Increment the control variable after each iteration

For Loop Examples

for (int i = 1; i <= 10; i++)
   System.out.print(i);

  12345678910
for (int j = 8; j < 1; j--)
   System.out.print(i);		  8765432
// Braces are needed when there are multiple
// statements in the loop

for (int count = 1; count <= 20; count++)
{
   System.out.print(count + "\t");
   if (count % 4 == 0)
      System.out.println();
}		 1     2     3     4
5     6     7     8
9     10    11    12
13    14    15    16
17    18    19    20    
// This is an example of a nested for loop

for (int x = 1; x <= 8; x++)
{
   for (int j = 1; j <= x; j++)
      System.out.print("*");

   System.out.println();
}		 *
**
***
****
*****
******
*******
********


Exercises

1. Create a program named sentence.java.  Ask the user to enter a sentence.  Output the number of vowels, consonants, and words in the sentence.

Hint:  Create int variables V, C, and W.  Create a for loop that steps through each character in the sentence and increments the appropriate variable.

2. Create a program named forloop.cpp.  Declare the following arrays:

double[] HourlyWage = {7.25, 10.75, 12.0, 8.55, 9.5, 20.0, 15.0, 11.75};
String[] Employees = {"Sam", "Ben", "Joie", "Holly", "Marcus", "Mini", "Max", "Tosh"};

Write a for loop that steps through each element of the arrays.  Output each employees, name and hourly wage.  Output the sum of all hourly wages.  Output the average hourly wage.

3. Create a program named roman.java.  Ask the user to enter a Roman Numeral.  Output the numeric value of the Roman Numeral.
Test your program with these numbers:  MCMXLII, MCMLXIX, DCCCLXXXVIII

Hint: Create a for loop that steps through each character of roman numeral. 

M = 1000, D = 500, C = 100, L = 50, X = 10, V = 5, I = 1.  
MDCLXVI = 1000 + 500 + 100 + 50 + 10 + 5 + 1 = 1666

If a digit is out of order, then it is subtracted from the next digit.  This is only used for these combinations:
CM = 900, CD = 400, XC = 90, XL = 40, IX = 9, IV = 4