Synopsis
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In this class we covered counter control and meta data loops and how to translate them. We're also introduced to the boolean data type and decision making with it.
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The boolean Data Type
Name: boolean
Values: true, false
Operators: & & (and)
| | (or)
! (not)
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and & &
ttline {1} {< boolean > & & < boolean > - > < boolean >}
returns true if both inputs are true, false if not.
Ex:
boolean x = true;
boolean y = false;
boolean z = x & & y; / /z evaluates to false
boolean w = x & & x; / /w evaluates to true
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Ex:
int a = IO.read_int (); / /a - > 7
int b = IO.read_int (); / /b - > 4
int c = IO.read_int (); / /c - > 10
boolean x = (a < c) & & (a < b); / /a < c - true & a < b - false
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Assume the input stream is 7 4 10
What will the be the value of x?
false
OR | |
ttline {1} {< boolean > | | < boolean > - > < boolean >}
returns true if at least one input is true, false if not.
NOT!
ttline {1} {! < boolean > - > < boolean >}
returns ``the other boolean''
Way 3 - the comparison program
/ /Read 3 ints
int a = IO.read_int ();
int b = IO.read_int ();
int c = IO.read_int ();
/ /perform comparison and display results
if ((a < b) & & (b < c))
{
IO.println (a, b, c);
}
else if ((a < b) & & (c < b))
{
print (a, c, b);
}
else ---
there will be fore more cases!
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Definition
ITERATION is the act of repeating a construct, or a slight variation on a construct again and again in some controlled fashion.
REMARK
There are three main mechanisms of iteration.
- ``while''
- ``for'' - most specific
- recursion
Definition
a WHILE statement is a repetition construct in which the item that is to be repeated is done so until a condition is met or true.
Ex:
Read and write four integers.
Counter Control Loop
int i = 1;
while (i < = 4)
{
int x = IO.read_int ();
IO.println (x);
i = i + 1;
}
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Ex:
Read several non zero integers and print them.
IO example:
in:8 - 16 - 4 3 0
out:8 - 16 - 4 3 - end of program since 0 is entered
Meta data control loop
int number = IO.read_int ();
while (! (number == 0))
{
IO.println (number);
number = IO.read_int ();
}
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Definition
A COUNTER CONTROL LOOP is a repetition construct which is characterized by a priori (beforehand) knowledge of how many times the instruction block is to be run.
REMARK
Counter control loops are controlled by a counter which governs the behavior of the loop.
Definition
a DATA CONTROL LOOP is a repetition construct which is governed by ``metadata'' accompanying the data being processed.
Definition
INCREMENTAL PROGRAMMING is a programming methodology wherein one develops a program by writing a sequence of programs with the following properties:
- The first program in the sequence performs some essentially trivial task, but one which is fundamental to completion of the ultimate task.
- The last program in the sequence performs the task of ultimate interest.
- Each successor program performs a task only marginally more elaborate than its predecessor.
Ex:
P0 P1 P2 P3 .... Pn
P1 is the first successor of the base program P0 and so on.
INSERT DIAGRAM HERE!
Versioning - If P2 is screwed up we can fall back on P1 and proceed from there.
Problem:
Read three integers and display the difference between the largest and the smallest values.
Input Result
----- ------
8 15 9 7
50 - 6 10 56
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The sequence of programs will be...
- P0: Read and echo 3 integers.
- P1: Same as P0, plus determine and display the max value.
- P2: Same as P1, plus compute and display the difference.
- P3: Same as P2, plus compute and display the difference between the max & min values.
- P4: Same as P3, but delete all ``extra'' output.
