Question

double TotalMinute=300.0 double TotalMinutesAdded=1378.0

 double TotalMinute=300.0 double TotalMinutesAdded=1378.0  foreach(DataRow dr in ds.Tables[0].Rows)                 {                      //Add The above Timings to each Row's 2nd Column                     DateTime correctDate=Convert.ToDateTime(dr[2]);                      correctDate.AddMinutes(TotalMinute);                     correctDate.AddMinutes(TotalMinutesAdded);                      dr[2]=correctDate;                  }

Answer 1

As mentioned, due to DateTime objects being immutable you have to reassign the variable.

However, a point to note is that you can chain the manipulations as so:

correctDate = correctDate.AddMinutes(TotalMinute)                          .AddMinutes(TotalMinutesAdded);