Qstring bad index.

[gbtrl.]

/*qstring object/* newText = arg1;
 
    if(newText.size() > 0)
    if(newText[newText.length()-1].isLetter())
    {
        for(int i{0}; i < vowels.length()-1; i++)
        {
            if(newText[newText.length()-1] == vowels[i])
            {
                newText[newText.length()-1] = vowels[i+1];
                ui->lineEdit->setText(newText);
                return;
            }

/*qstring object/* newText = arg1;

    if(newText.size() > 0)
    if(newText[newText.length()-1].isLetter())
    {
        for(int i{0}; i < vowels.length()-1; i++)
        {
            if(newText[newText.length()-1] == vowels[i])
            {
                newText[newText.length()-1] = vowels[i+1];
                ui->lineEdit->setText(newText);
                return;
            }

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vowels[i+1] indexes the last element of the Qstring, not the element one over from i. Why is this?
Also, is there a shorter way to reference the last element of a Qstring.