Swapping characters pairs in a string
I haven't run the code, but are you sure it does as you expect it to for odd length strings? By padding the last character with a space, you get some... interesting results. 

For example, inputting "foo" will return "of o". That doesn't seem quite right to me. I would expect it to return "ofo".  I would do something like this. 

private string StringSwap(string stringToSwap)
{
    char[] array = stringToSwap.ToCharArray();

    // even size strings iterate the whole array
    // odd size strings stop one short 
    int offset = (stringToSwap.Length % 2)
    for (int i = 0; i &lt; array.Length - offset; i += 2)
    {
        char temp = array[i];
        array[i] = array[i + 1];
        array[i + 1] = temp;
    }
    return new String(array);
}


Essentially, when the mod of 2 equals zero, the code behaves exactly like yours does now, but when the mod of 2 equals one, the loop exits one iteration early, avoiding the IndexOutOfRangeException that prompted you to hack in that white space. 

Also note that I changed 

    return new string(array);


To

     return new String(array);


It's terribly picky and pedantic, but I find it poor form to use the string alias when you're using it as a class. Seeing a ctor called on a camelCased identifier just looks weird to me. Same goes for things like string.Empty. But, like I said, that's just me being nit picky and pedantic. It's not actually a problem.