#include <iostream>
#include <string>
using namespace std;
 
int main()
{
    size_t i, j, len;
    string str;
 
    cout << "Enter string: ";
    getline(cin, str);
 
    len = str.length();
 
    i = 0;
    while (i < len)
    {
        if (str[i] == ' ')
        {
            for (j = i + 1; j < len; ++j)
            {
                str[j - 1] = str[j];
            }
            --len;
        }
        else
            ++i;
    }
 
    str.resize(len);
 
    cout << str << endl;
 
    //system("pause");
    return 0;
}

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SGVsbG8gV29ybGQgICAgaXMgdGhpcyB3b3JraW5nPw==

Hello World    is this working?