What is the difference between using range in the first program and not using it in the second program?

For an assignment, I needed to make a program that counts the vowels and consonants in a string using for i in range(0, len(str)):

I put this program together using what I learned, but I can’t really wrap my head around why it works.

vowelCount = 0
consonantCount = 0

sentence = input("Enter your sentence: ")

for char in range(0, len(sentence)):
    if sentence[char] in "aeiouAEIOU":
        vowelCount += 1
    if sentence[char] in "bcdfghjklmnpqrstvwxyBCDFGHJKLMNPQRSTVWXYZ":
        consonantCount += 1

print("There are", vowelCount, "vowels")
print("There are", consonantCount, "consonants")

Why am I getting the range of the length of the sentence?

Here’s an alternative program I wrote without the range.

vowelCount = 0
consonantCount = 0

sentence = input("Enter your sentence: ")

for i in sentence: 
    if i in "aeiouAEIOU":
        vowelCount += 1
    if i in "bcdfghjklmnpqrstvwxyBCDFGHJKLMNPQRSTVWXYZ":
        consonantCount += 1

print("There are", vowelCount, "vowels")
print("There are", consonantCount, "consonants")

Why do I need to use sentence[char] in the range version? Why the brackets?

>Solution :

Your program is going through sentence one letter at a time. For each letter (retreived by sentence[char]) it checks whether it is in the list of vowels (if yes, increment vowelCount) or in the list of consonants (if yes, increment consonantCount).

The form a in b for strings a and b checks whether a is contained somewhere as exact substring in b. So if a is just a single letter, it checks whether b contains the letter a anywhere.