Question

NEED TUT IN LOOPING

Asked by: joy333

I want to learn all the aspects of looping!
need some tut in looping!

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Asked On
2004-06-10 at 21:02:08ID21021841
Topic

Miscellaneous Programming

Participating Experts
3
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Answers

 

by: drnickPosted on 2004-06-10 at 21:40:03ID: 11285880

there are 3 basic types of loops in most programming languages:

the FOR-type
with this loop, you run through a specific piece of code clearly definid times

example:

for(int i = 0; i < 10; i++)      
 {
 printf("%d\n", i);
 }

will print the numbers from 0 to 9, because the loop's body will be executed 10 times,
since i is zero at the beginning and is incremented AFTER each pass.

the WHILE-type

While loops have a loop condition which is always checked at the beginning.

int i = 2;
while(i > 0)
  {
 printf("%d\n", i);
 }

will print 2 and 1.


the DO-loops (also often REPEAT/UNTIL)

int i = 2;
do
 {
 printf("%i\n");
} while(i > 0);

Will print 2, 1 and 0, because the loop's condition is at the loops bottom
and checked after each pass (in contrast to while-loops).

Note that you can translate all these loops into each other.

Some Languages also support FOR-EACH-loops,
which allow you to do an action for every item in a collection.

These were loops in High Level Languages (HLL).

However, a processor often doesn't support loop constructs,
so in machine code, loops are most commonly translated to
conditional jumps, which also can be used in most HLL:

int i = 2;
here: //label
printf("%d\n", i);
i--;
if(i >= 0) goto here; //jump

The intel 80x86 processor also support a special, optimized loop
statement for a special register (ECX/CX/CL) (which thus cannot be used
for nested loops):

MOV EAX, 1
MOV ECX, 100
@label:
INC EAX
LOOP @label

which will count ECX down to 0 while incrementing EAX up to 101.

 

by: drnickPosted on 2004-06-10 at 21:40:21ID: 11285883

if you've any further questions, let me know

 

by: PreachDotNetPosted on 2004-06-11 at 06:55:39ID: 11288635

in vb
For i = 1 to 50
  'do stuff
next i

do while i < 51
   'do more stuff
loop

loops can be exited using the Exit for and exit do function
for i = 1 to 50
   if i = 4 then
      exit for
   end if
i=i+1
next i

Loops can be nested
For each row in rows
   for each col in columns
      debug.write row,col
   next col
next row

loops cant be step nested
for each row in rows
   for each col in cols
       debug.write row,col
   next row
next col

Loops can also be infinite
i=1
Do while i > 0
  i=i+1
loop
Ctrl & Break will rescue you....

Loops are useful to use with collections
dim dr as datarow
for each dr in dataset.tables(0).rows
   debug.print dr("ThisField")
next dr

Everything inside a loop should be indented for clarity and so u can quickly see where the loop begins and ends

Sorry for cutting in drnick but I thought id give a more basic explanation....  Thanks for the assembler revisited though :? i knew there was a reason I never used it ;)

 

by: drnickPosted on 2004-06-11 at 08:10:17ID: 11289405

yeah, i think we made a good picture of loops today, my friend.
i didn't intend to make he/she an assembler geek (like mine was),
but wanted to give a clear view of: that's how you see it in your hll,
and that's how it's done below.
with .net we made it from basics to the top, that's quite perfect.

 

by: jzanettePosted on 2004-06-22 at 03:10:47ID: 11367577

When writing Shell Scripts (batch files) for Windows NT, 2000, XP and Server 2003, see the FOR command is used for looping.  See the cross-platform syntax at

   (http://TheSystemGuard.com/TheGuardBook/CCS-Int/FOR.htm)

An example of using a FOR loop is at

   (http://BoomingOrFuming.com/Booming/THE%20FIRING%20ISSUE%20-%2020030108.htm)

See "The Labyrinths of FOR" about halfway down the page.

20120131-EE-VQP-002

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