Write a program that converts strings of all uppercase characters into strings of all lowercase and viceversa

Sure, here is a simple Python program that converts strings of all uppercase characters into strings of all lowercase and vice versa:

def convert_case(s):
    new_str = ''
    for char in s:
        if char.isupper():
            new_str += char.lower()
        elif char.islower():
            new_str += char.upper()
        else:
            new_str += char
    return new_str

# Test the function
print(convert_case('Hello WORLD'))

In this program, we define a function convert_case(s) that takes a string s as input. We initialize an empty string new_str. Then, for each character in the input string, we check if it is uppercase or lowercase. If it is uppercase, we convert it to lowercase and add it to new_str. If it is lowercase, we convert it to uppercase and add it to new_str. If the character is neither uppercase nor lowercase (for example, a space or punctuation), we just add it to new_str as it is. Finally, we return new_str.

The line print(convert_case('Hello WORLD')) is used to test the function. It should print hELLO world.