3. Calculate the number of characters: write a program to receive a character string and a character composed of letters, numbers and spaces, and then output the number of characters contained in the input character string, regardless of case. Input: ABAOP123 A. Output: 2. 4. Enter a line of characters and count the numbers of English letters, spaces, numbers and other characters.

Here are two programs - one for calculating the number of a specific character in a string, and another for counting the number of different types of characters in a string:

Program 1: Counting the number of a specific character in a string

string = input("Enter a string: ")
char = input("Enter a character: ")

count = 0

for c in string:
    if c.lower() == char.lower():
        count += 1

print(f"The string '{string}' contains {count} instances of the character '{char}'.")

Program 2: Counting the number of different types of characters in a string

string = input("Enter a string: ")

num_letters = 0
num_spaces = 0
num_numbers = 0
num_other = 0

for c in string:
    if c.isalpha():
        num_letters += 1
    elif c.isspace():
        num_spaces += 1
    elif c.isdigit():
        num_numbers += 1
    else:
        num_other += 1

print(f"The string '{string}' contains:")
print(f"- {num_letters} letters")
print(f"- {num_spaces} spaces")
print(f"- {num_numbers} numbers")
print(f"- {num_other} other characters")