"""
A module to show off loop invariants in a function

Authors: Walker M. White (wmw2), Lillian Lee (LJL2), Steve Marschner (srm2)
Date:    November 1, 2017 (Python 3 Version)
"""
import sys


def num_adj_pairs(s):
    """
    Returns: number of adjacent equals pairs in s
    
    An adjacent pair has the form s[k-1], s[k].
    Example: num_adj_pairs('ebeee') is 2
    
    Parameter s: the string to search
    Precondition: s is a string
    """
    # Set x to # adjacent equal pairs in s[0..len(s)-1]
    
    x = 0
    k = 1
    # inv: x = # adjacent equal pairs in s[0..k-1]
    while k < len(s):
        # Process k
        print('loop:', x, 'pairs in', s[0:k])
        if (s[k-1] == s[k]):
            x = x + 1
        k = k + 1
    
    # x = # adjacent equal pairs in s[0..len(s)-1]
    print('post:', x, 'pairs in', s)
    return x


if __name__ == '__main__':
    assert len(sys.argv) == 2
    s = sys.argv[1] # get string from command line
    x = num_adj_pairs(s)
    print('The number of matching adjacent pairs in ' + repr(s) + ' is '+str(x))