CMIS 102 
for loops

--for loop preferred over while loop when know at start of loop execution how many
iterations are to be done.  "definite iteration".
vs.
--while loop preferred over for when don't know at start of loop execution how many
iterations are to be done.  "indefinite iteration".

Typical use of for

for variable in range(number):
    statement(s) of body

will loop 'number' times, with 'variable' going from 0 to number-1.
'Number' is usually an int variable or an int expression.

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#user tells how many numbers to input and sum

n = eval(input("Enter number of numbers: "))
sum = 0
for count in range(n):      #loop n times, the most common loop in the universe
    num = eval(input("Enter a number: "))
    sum += num
print("Sum is", sum)
#Do: display the value of count each iteration


#range(start,end)    loops from start to end-1

n = eval(input("Enter number of numbers: "))
sum = 0
for count in range(1,n+1):      #loop n times, the most common loop in the universe
    num = eval(input("Enter number #"+str(count)+": "))
    sum += num
print("Sum is", sum)

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#sum of the first N integers
n = eval(input("Enter n: "))
sum = 0
for i in range(1,n+1):     #'i' index, iteration variable
    sum += i
print(sum)


#display the first N perfect squares.
n = eval(input("Enter n: "))
for i in range(1,n+1):
    print(i, ":", i*i)


#input numbers from user. Display that number of *'s, one per line.
#Negative number indicates end. 
num = eval(input("Enter a number: "))    #first number from user
while num >= 0:        #until a negative number is entered
    for stars in range(num):
        print("*")
    num = eval(input("Enter a number: "))



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#Fahrenheit to Celsius table.  range has 3rd argument: step

print("F   C")
for tempF in range(-40,130,10):   #by 10s
    print(tempF, round(5.0/9.0*(tempF-32)))   #round to integer


Counting down loop: step argument negative

print("F   C")
for tempF in range(120,-50,-10):   #by -10s
    print(tempF, round(5.0/9.0*(tempF-32)))   #round to integer



#sum of the first N Harmonic numbers (1/1 + 1/2 + 1/3 + 1/4 + ... + 1/N)
n = eval(input("Enter N: "))
sum = 0
for i in range(1,n+1):
    sum += 1 / i
print(sum)      #diverges (goes to infinity)


#sum of the reciprocals of powers of 2 (1/2^0 + 1/2^1 + 1/2^2 + 1/2^3 + ... + 1/2^N)
#                                      (1/1   + 1/2   + 1/4   + 1/8   + 1/16
#Achilles/arrow paradox
n = eval(input("Enter N: "))
sum = 0
for i in range(0,n+1):
    sum += 1 / 2**i
print(sum)      #converges to what?


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Can loop over the characters of a string:
s = "yabba dabba doo"
for c in s:
    print(c)


#count categories of characters
s = "yab@#$%^ba daBBa D12oo"
uppers = lowers = digits = others = 0
for c in s:
    if c.isupper():      #str.isupper()   true if is/are uppercase letter(s)
        uppers += 1
    elif c.islower():
        lowers += 1
    elif c.isdigit():
        digits += 1
    else:
        others += 1
print("#uppers:",uppers," #lowers:",lowers," #digits:",digits," #others:",others) 



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if the loop control variable is not used in the body of the loop,
can use _ instead

for _ in range(n):     
    num = eval(input("Enter a number: "))
    sum += num