3. 使用 for in 语句,while 语句,以及 for in range ()语句,等 3 种方 式,统计用户输入的字符串中,字母和数字的个数。并给出测试用例。

在Python中，有多种方法可以统计用户输入的字符串中字母和数字的数量。以下是三种常见方式：

1. **for in 语句（遍历字符串每个字符）**:

def count_chars(input_str):
    count = {'letters': 0, 'numbers': 0}
    for char in input_str:
        if char.isalpha():
            count['letters'] += 1
        elif char.isdigit():
            count['numbers'] += 1
    return count

test_case_1 = "Hello123"
print(count_chars(test_case_1))

2. **while 语句（手动迭代直到遍历完字符串）**:

def count_chars_manual(input_str):
    count = {'letters': 0, 'numbers': 0}
    index = 0
    while index < len(input_str):
        char = input_str[index]
        if char.isalpha():
            count['letters'] += 1
        elif char.isdigit():
            count['numbers'] += 1
        index += 1
    return count

test_case_2 = "Python456"
print(count_chars_manual(test_case_2))

3. **for in range() 语句（适用于已知长度的字符串）**:

def count_chars_range(input_str):
    count = {'letters': 0, 'numbers': 0}
    for i in range(len(input_str)):
        char = input_str[i]
        if char.isalpha():
            count['letters'] += 1
        elif char.isdigit():
            count['numbers'] += 1
    return count

test_case_3 = "ABC123 DEF456"
print(count_chars_range(test_case_3))

上述测试用例的结果将分别返回包含字母和数字个数的字典。