採用氣泡排序（穩定排序）：

法1： 遇到非字母字元時，處理要小心。

#include<iostream>
#include<string>
using namespace std;
int main()
{
    string s,str;
    char tempc;
    while(getline(cin,str))
    {
        int len = str.length();
        for(int i = 0; i < len; i++)
        {
            for(int j = 0; j< len-i-1; j++)
            {
                int k = j;
                if(isalpha(str[j]))
                {
                    while(k < len-1 && !isalpha(str[k+1]))
                        k++;
                    if(k == len-1)
                        continue;
                    if(tolower(str[j]) > tolower(str[k+1]))
                    {
                        tempc = str[j];
                        str[j] = str[k+1];
                        str[k+1] = tempc;
                    }
                }
                else
                    continue;
            }
        }
        cout << str << endl;
    }
    return 0;
}


 

法2：藉助額外的空間來處理

#include <iostream>
#include <string>
using namespace std;

int main()
{
	string str;
	char tempc;
	while (getline(cin, str))
	{
		string s;
		for (int i = 0; i<str.size(); i++)
		{
			if (isalpha(str[i]))
				s += str[i];
		}
		for (int i = 0; i<s.size(); i++)
		{
			for (int j = 0; j<s.size() - i - 1; j++)
			{
				if (tolower(s[j]) > tolower(s[j + 1]))
				{
					tempc = s[j];
					s[j] = s[j + 1];
					s[j + 1] = tempc;
				}
			}
		}
		for (int i = 0, j = 0; i<str.size(); i++)
		{
			if (isalpha(str[i]))
				str[i] = s[j++];
		}
		cout << str << endl;
	}
	return 0;
}