Common application scenarios of ASCII in programming - 面试题

Common application scenarios of ASCII in programming:

1. Character Validation:

python
# Check if character is a letter
def is_letter(char):
    return 'A' <= char <= 'Z' or 'a' <= char <= 'z'

# Check if character is a digit
def is_digit(char):
    return '0' <= char <= '9'

# Check if character is printable
def is_printable(char):
    return 32 <= ord(char) <= 126

2. Character Conversion:

python
# Case conversion
def to_upper(char):
    if 'a' <= char <= 'z':
        return chr(ord(char) - 32)
    return char

def to_lower(char):
    if 'A' <= char <= 'Z':
        return chr(ord(char) + 32)
    return char

3. String Processing:

python
# Remove whitespace characters
def trim_whitespace(s):
    return s.strip()  # Remove space(32), tab(9), newline(10/13), etc.

# Count character types
def count_chars(s):
    letters = digits = others = 0
    for c in s:
        if 'A' <= c <= 'Z' or 'a' <= c <= 'z':
            letters += 1
        elif '0' <= c <= '9':
            digits += 1
        else:
            others += 1
    return letters, digits, others

4. Data Encoding:

python
# Base64 encoding (based on ASCII)
import base64
encoded = base64.b64encode(b'Hello').decode('ascii')

# URL encoding
from urllib.parse import quote
encoded = quote('Hello World', safe='')

5. Network Protocols:

HTTP headers use ASCII encoding
SMTP, FTP and other protocols are based on ASCII
JSON strings use ASCII characters

6. File Processing:

python
# Read ASCII text file
with open('file.txt', 'r', encoding='ascii') as f:
    content = f.read()

Important Notes:

Use Unicode when handling non-ASCII characters
Pay attention to line ending differences (CRLF vs LF)
Validate input character validity