jhon thank you so much now with your details I've understand the meaning of it
I've changed the code here
float temp = sensors.getTempCByIndex(0);
Serial.println(temp,DEC);
char buffer[10];
// itoa(temp,buffer,10);
dtostrf(temp, 5, 2, buffer);
ht1632_putchar(6 , 8, buffer[0]);
ht1632_putchar(12 , 8, buffer[1]);
ht1632_putchar(18 , 8, buffer[2]);
ht1632_putchar(24 , 8, buffer[3]);
ht1632_puttinychar(32 , 8, 'o');
ht1632_putchar(37 , 8, 'C');
delay(150);
now works perfectly
many thanks