beginner question

[Naito]

hi guys can you please help me understand the difference bteween these 2 codes?
my interpretation is def function has a loop in it (im not smart)

def func(x):
  res = 0
  for i in range(x):
     res += i
  return res

print(func(5))

output is 10

and

def func(x):
  for i in range(x):
     res = 0
     res += i
  return res

print(func(5))

output is 4
thanks for helping me