Take a look at QMessageBox(). The text you wish to display is passed as one of the params to the constructor(s). The following example is a snippet of code from a recent project (note the single comma for multiple lines of quoted text -- all the text is part of a single parameter).
QMessageBox::information ( 0, "SoftHHT",
"One or more expected Saved Settings missing.\n\n"
"Did NOT automatically initialize operator stations.\n\n",
QMessageBox::Ok || QMessageBox:
efault, QMessageBox::NoButton,
QMessageBox::NoButton );
