Thank you for your help. I finally got it to work. This is the code which worked for me.
int reading = analogRead(sensorPin);
float voltage = reading * 5.0;
voltage /= 1024.0;
float temperatureC = (voltage) * 100;
char buffer[10];
String tem = dtostrf(temperatureC, 5, 2, buffer);
String temper = (tem);
Here is the chart: https://www.thingspeak.com/channels/1531/charts/2
Once again, thank you.