Problem with print variable in print.cell (fpdf)

[muconi]

Hi, i have problem with printing result from some simple example in pdf file?
pdf.cell(200, 10, "Nesto stampam" + c_string, 1, 0)

import sys
import fpdf

from PyQt6 import QtWidgets, uic
from fpdf import FPDF

qtcreator_file  = "testna_forma.ui" # Enter file here.
Ui_Prozor, QtBaseClass = uic.loadUiType(qtcreator_file)


class MyApp(QtWidgets.QDialog, Ui_Prozor):
    def __init__(self):
        QtWidgets.QMainWindow.__init__(self)
        Ui_Prozor.__init__(self)
        self.setupUi(self)

        self.Izracunaj_dugme.clicked.connect(self.Izracunaj_sve)
        self.Stampaj_pdf.clicked.connect(self.Stampaj)

    def Izracunaj_sve(self):
           
           a = float(self.unesi_a.text())
           b = float(self.unesi_b.text())

           c = a + b
           d = a - b
           e = a * b
           f = a / b
            
           self.prikazi_c.setText(format(c))
           self.prikazi_d.setText(format(d))
           self.prikazi_e.setText(format(e))
           self.prikazi_f.setText(format(f))
           print(c)
           print(d)
           print(e)
           print(f)
           c_string = str(c)
           d_string = str(d)
           e_string = str(e)
           f_string = str(f)

    def Stampaj(self):

           pdf = FPDF('P', 'mm', 'A4')
           pdf.add_page()
           pdf.set_font('Arial', 'B', 12)
           pdf.cell(200, 10, "Nesto stampam" + c_string, 1, 0)
           #pdf.write(5,'Nesto stampam')
           pdf.output("Izvjestaj.pdf", 'F')

if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    window = MyApp()
    window.show()
    sys.exit(app.exec())