统计字符串中字母、数字、空格和其他字符的个数C++

可以使用C++中的isdigit()、isalpha()和isspace()函数来判断字符是否为数字、字母和空格，其他字符可以通过排除这些情况来计算。以下是一个示例代码：

#include <iostream>
#include <string>

using namespace std;

int main()
{
    string str = "Hello World! 123";
    int letter_count = 0, digit_count = 0, space_count = 0, other_count = 0;

    for (int i = 0; i < str.length(); i++)
    {
        if (isalpha(str[i]))
            letter_count++;
        else if (isdigit(str[i]))
            digit_count++;
        else if (isspace(str[i]))
            space_count++;
        else
            other_count++;
    }

    cout << "Letter count: " << letter_count << endl;
    cout << "Digit count: " << digit_count << endl;
    cout << "Space count: " << space_count << endl;
    cout << "Other count: " << other_count << endl;

    return 0;
}

输出：

Letter count: 10
Digit count: 3
Space count: 3
Other count: 2