1. The for-statement

2. Previously discussed: different loop-statements in Java
Java provides 3 types of loop-statements:
We will now study the for-statement
1. The while-statement
2. The for-statement
3. The do-while-statement  

3. Previously discussed: find all divisor of a number n
Algorithm to find all divisors of a number n:
The variable x takes on the values 1, 2, 3, ..., n one at a time
For each value, we check whether n is divisible by x
If so, we print the value x (and obtain all divisors)
for (x = 1, 2, 3, ..., n) do {
if ( n is divisible by x )
print x; // x is a divisor of n }

4. The for-statement
The for-statement is ideally suited for making the following type of program:
The for-statement can best be explained with an example....
Let some variable x take on a series of value one at a time
For each value taken on by a variable x, the body of the for-statement is executed once.

5. Example for-statement: the most common way to use a for-statement
The for-statement was originally invented to let some variable take on a series of value

6. Example for-statement: the most common way to use a for-statement (cont.)
The most common form of the for-statement is as follows:
for ( var = START_VALUE ; var <= STOP_VALUE ; var = var + INCR ) {
/* for-body (statements) */ }

7. Example for-statement: the most common way to use a for-statement (cont.)
Meaning:
The variable var will take on the following values:
For each of the value, the statements in the for-body are executed
START_VALUE
START_VALUE + INCR
START_VALUE + 2×INCR
...
Up to the largest value that is ≤ STOP_VALUE

8. Example for-statement: the most common way to use a for-statement (cont.)
public class For01 {
public static void main(String[] args)
int a;
// Example "for-statement"
for ( a = 1 ; a <= 10 ; a = a + 1 )
System.out.println(a); // Print a }
System.out.println("Done");
Output: 1
2 (1+1×1)
3 (1+2×1)
4 (1+3×1)
5 (1+4×1)
6 (1+5×1)
7 (1+6×1)
8 (1+7×1)
9 (1+8×1)
10 (1+9×1)
Done

9. Example for-statement: the most common way to use a for-statement (cont.)
Notice that in the for-statement:
a = 1 specifies the starting value
a <= 10 specifies when the for-loop will stop
a = a + 1 specifies how the variable a will change each time through the loop

10. Example for-statement: the most common way to use a for-statement (cont.)
Example Program: (Experiment with it yourself outside class !)              
Prog file:
How to run the program:            
Right click on link and save in a scratch directory
To compile:   javac For01.java
To run:          java For01

11. Example for-statement: the most common way to use a for-statement (cont.)
Example 2: changing the START_VALUE
public class For01 {
public static void main(String[] args)
int a;
// Changing the starting value:
for ( a = 5; a <= 10; a = a + 1 )
System.out.println(a); // Print a }
System.out.println("Done");
Output: 5
6 (5+1×1)
7 (5+2×1)
8 (5+3×1)
9 (5+4×1)
10 (5+5×1)
Done

12. Example for-statement: the most common way to use a for-statement (cont.)
Notice that in the for-statement:
a = 5 specifies the starting value
a <= 10 specifies when the for-loop will stop
a = a + 1 specifies how the variable a will change each time through the loop

13. Example for-statement: the most common way to use a for-statement (cont.)
Example 3: changing the STOP_VALUE
public class For01 {
public static void main(String[] args)
int a;
// Changing the continuation condition:
for ( a = 1; a <= 3; a = a + 1 )
System.out.println(a); // Print a }
System.out.println("Done");
Output: 1
2 (1+1×1)
3 (1+2×1)
Done

14. Example for-statement: the most common way to use a for-statement (cont.)
Notice that in the for-statement:
a = 1 specifies the starting value
a <= 3 specifies when the for-loop will stop
a = a + 1 specifies how the variable a will change each time through the loop

15. Example for-statement: the most common way to use a for-statement (cont.)
Example 4: changing the INCR (increment) value
public class For01 {
public static void main(String[] args)
int a;
// Changing the increment statement:
for ( a = 1; a <= 10; a = a + 2 )
System.out.println(a); // Print a }
System.out.println("Done");
Output: 1
3 (1+1×2)
5 (1+2×2)
7 (1+3×2)
9 (1+4×2)
Done

16. Example for-statement: the most common way to use a for-statement (cont.)
Notice that in the for-statement:
a = 1 specifies the starting value
a <= 10 specifies when the for-loop will stop
a = a + 2 specifies how the variable a will change each time through the loop: increment by 2!!

17. Example for-statement: the most common way to use a for-statement (cont.)
Class exercise: what is the output of this for-loop
public class For01 {
public static void main(String[] args)
int a;
// Changing the increment statement:
for ( a = 4; a <= 14; a = a + 3 )
System.out.println(a); // Print a }
System.out.println("Done");

18. Example for-statement: the most common way to use a for-statement (cont.)
Answer: 4
7 (4 + 1×3)
10 (4 + 2×3)
13 (4 + 3×3)
Done

19. Syntax and meaning of the for-statement
The general syntax of the for-statement is as follows:

20. Example for-statement: the most common way to use a for-statement (cont.)
Because:
We start with the value 4
We increase the value with 3 each time
Hence: 4, 7, 10, 13
The next value in the series is 16, but 16 is not ≤ So we stop

21. Syntax and meaning of the for-statement (cont.)
Explanation:
The keyword for announces (to the Java compiler) that we started an for-statement
Following the keyword for, there are 3 clauses:
1. An init-statement: this is a statement that is executed once at the start of the for-statement

22. Syntax and meaning of the for-statement (cont.)
2. A LOOP-CONTINUATION-CONDITION: this is a Boolean expression that determines whether the for-statement will be terminated
(This clause has the same function as in the LOOP-CONTINUATION-CONDITION of an while-statement)
3. A INCR-STATEMENT: this is a statement that is executed at the end of the loop.

23. Syntax and meaning of the for-statement (cont.)
The INCR-STATEMENT is executed:
After the for-loop body
Before the for-statement repeats to test the
LOOP-CONTINUATION-CONDITION

24. Syntax and meaning of the for-statement (cont.)
The for-statement is completed with one statement
This is the body of the for-statement
The body will be executed as long as the loop-continuation-condition is true !!!      
After the body has been executed, the INCR-STATEMENT is executed before repeating the check of the LOOP-CONTINUATION-CONDITION

25. Common practice in for-statements
Common practice in for-loops:
Use a block as body of for-statements

26. Common practice in for-statements (cont.)
A typical for-loop looks like this:

27. Flow chart of a for-statement
(I have used colors to highlight the correspondence of the pieces in the Java language syntax and in the flow chart)

28. Flow chart of a for-statement (cont.)
Flow chart representing the for-statement:

29. Flow chart of a for-statement (cont.)
This is the program flow when LOOP-CONTINUATION-CONDITION is true:

30. Flow chart of a for-statement (cont.)
In this case, the for-statement will:
Execute the statements in the body
Execute the INCR-STATEMENET
Repeat the for-statement from the LOOP-CONTINUATION-CONDITION

31. Flow chart of a for-statement (cont.)
This is the program flow when LOOP-CONTINUATION-CONDITION is false:

32. Flow chart of a for-statement (cont.)
In this case, the for-statement will:
Terminate
The program will proceed with the statement that follows the for-statement

33. Flow chart of a for-statement (cont.)
Example:
for ( a = 1 ; a <= 10 ; a++ ) {
System.out.println(a); }
System.out.println("Done");

34. Flow chart of a for-statement (cont.)
Flow chart of this program:

35. Flow chart of a for-statement (cont.)
Note: this is the same flow chart we saw before belonging to this program fragment:
a = 1;
while ( a <= 10 ) {
System.out.println(a);
a++; }
System.out.println("Done");

36. Flow chart of a for-statement (cont.)
Execution:
Program "loops" as long as a ≤ 10
Program exits loop when a > 10

37. Structure diagram of a for-statement

38. Structure diagram of a for-statement (cont.)
Structure diagram representing a while-statement:

39. Structure diagram of a for-statement (cont.)
How to "read" the diagram:
The outer rectangle containing the LOOP-CONTINUATION-CONDITION represents the for-statement:

40. Structure diagram of a for-statement (cont.)
The for-statement is one (single) statement)
The for-statement will only complete execution when the LOOP-CONTINUATION-CONDITION becomes false

41. Structure diagram of a for-statement (cont.)
The inner rectangle (shaded with a green color) is the while-loop body
When the LOOP-CONTINUATION-CONDITION is true, the for-statement will execute:
The statements in the inner rectangle (the for-statement's body)
The INCR-statement