review condition and loop

conditional statement:   if-then-else
if cond :  
   do-true
else:
   do-false

if 3 > 2 :
  print("yes")
else:
  print("no")

loop

while-loop

while cond :
  do-loop

i = 5
while i > 0 :
  print(i)
  i = i - 1

function range() is used to specify the range of value.  Mostly it is used to iterate the loop.

range() returns  list of integers
range(n)  returns [0,n)  with increment 1

range(4) -->  0,1,2,3

range(start,stop,step)

range(1,10,2)  -->  1,3,5,7,9

Observe what values this snippet of code print out.

x = 0
while x in range(10):
  print(x)
  x = x + 1

change the above program so that it prints 10.

for-loop

for x in range(10)
  print(x)

It is a bit more compact than while-loop. initial x and increment is automatic.

try

for x in range(1,10,2)
  print(x)

The above code is similar to this while-loop, observe the initialize of variable and its increment.

x = start
while x < stop
  do-body
  x = x + step

Flow chart

We draw flowchart to prime our brain into the habit of breaking a big problem into smaller steps.  Somebody may find "pseudo code" is easier to work with.  I found that for "spatial" type of thinker, diagram works very well.  Try it anyway at least to know what type you prefer.

  sequential
  if-then-else
  while-loop
  for-loop

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