How to you make a number squared in C#?

I have looked around to the answer to this question, but i cant seem to find a way. I know i can multiply the number by itself, but that would add a complication that i may not know how to fix with my basic coding knowledge.

I am basicly trying to find the area of a circle and the eqation is πr(squared). I just dont know how to square my math equation. Here is the part of the script where i am doing the math.

(the numbers were entered into inputfield boxes so i had to convert it in the first 3 statements.)

public void Product() {
		int a = Convert.ToInt32(t1.text);
		int b = Convert.ToInt32(t2.text);
		int c = Convert.ToInt32 (t3.text);
		int d = a/2*3.14;
		Result.text = d.ToString ();
	}
	
}

pi is of course an infinitely large number of decimals, unity contains a close approximation

mathf also has a function called pow which takes a number raised to a power

float radius;
radius = ...(decide yourself)
float area = Mathf.Pow(Mathf.Pi * radius, 2);

now area equals pi * radius squared

alternately

float radius;
radius = ...(decide yourself)
float area = 3.14159 * radius;
area = area * area;

or

float area = 3.14159 * radius;
area *= area;

or

area = (3.14159 * radius) * (3.14159 * radius);

or

basically you can either use mathf.pi instead of 3.14159 or any other approximation of pi.

and you can manually do the math yourself or use the function

mathf.Pow( number to raise to a power, power to raise to);

so

mathf.Pow(2, 2)
equals
4

mathf.Pow (2, 3)
equals
8

mathf.Pow (3.14159 * radius, 2)
equals
area of a circle

Method 1 (as Mehul Rughani stated):

float area = Mathf.pi * radius * radius;

Method 2 (less efficient for only a square, but potentially more scalable otherwise):

float area = Mathf.pi * Mathf.Pow(radius, 2.0f);