"""
This program:
- asks the user to enter a string.
- verifies that the string represents an integer, and has the format:
- [optional] white space at the start
- [optional] minus sign
- a sequence of consecutive characters of digits, from 0 to 9.
- [optional] white space at the end

This is a simpler implementation of verify_integer1.py, with the same
functionality, by stripping white space from the beginning and end
of the string.
"""

import string #importing some useful string methods

my_string = input("enter a string: ")

# this line removes whitespace from the beginning and the end.
my_string = my_string.strip()

print("checking if", my_string, "is an integer...")

position = 0

# we will set illegal_flag to true if we find proof that the string is
# not a valid integer
illegal_flag = False

# skip any minus sign at the beginning
if position < len(my_string):
    character = my_string[position]
    if character == "-": #skip minus sign
        position = position + 1

# we now should get a string of consecutive digits. Let's count how many.
digit_count = 0
while position < len(my_string):
    character = my_string[position]
    if character in "0123456789":
        position = position + 1
        digit_count = digit_count + 1
    else:
        illegal_flag = True
        print("illegal character found:", character)
        break

if digit_count == 0:
    illegal_flag = True
    
if (illegal_flag == True):
    print("String", my_string, "is not a valid integer.")
else:
    print("Verified string", my_string, "as a valid integer.")