How can i add CPU temperature in C#

You can use WMI class to get cpu temperature

First, add a reference to System.Management.dll

To get cpu temperature you can use the query following

double temperature = 0;
string instanceName = "";

ManagementObjectSearcher searcher = new ManagementObjectSearcher(@"root\WMI", "SELECT * FROM MSAcpi_ThermalZoneTemperature");

foreach (ManagementObject obj in searcher.Get())
{
    temperature = Convert.ToDouble(obj["CurrentTemperature"].ToString());
    // Convert your value to celsius degrees
    temperature = (temperature - 2732) / 10.0;
    instanceName = obj["InstanceName"].ToString();
}
Console.WriteLine(temperature);
Console.WriteLine(instanceName);

and don't forget add using to System.Management.