code for percentage calculation in c#

A general solution to ensure that a rounded collection of numbers still adds up to the same as it did before is quite difficult. However, I think you are just doing two numbers, so one is 100% minus the other:

int boys_pc = (int)(0.5f + ((100f * boys_count) / total_count));
int girls_pc = 100 - boys_pc;

Cast to float to avoid integer division giving you a zero, and add 0.5 for integer rounding. Use 0.5f not 0.5 to keep it from expanding to double (which is overkill for something which will be rounded to int anyway).

Edit: If you have to multiply anyway, just multiply by a float constant (e.g. 100f not 100) to avoid integer division.

Use

System.Math.Round()

method.

Use Math.Round(56.8) will be 57

You can use ToString to format how you want the display.
So if you have

double percent;
...
percent = 29.8;

...

public string PercentDisplay
{
    get{return percent.ToString("00")} //Will always show 2 digits and no decimal
}

In comparison if you always wanted 2 decimal places (even if they are 0's) you can code like this percent.ToString("00.00")

percentage should be calculate by below formula

count = ((count / totalcount)*100);