C :: User Defined Number Of Decimal Places?

I need the user to be able to input the number of decimal places they wish to have displayed in the output. Everything works fine as is, I just don't know how to allow for the user to input the number of decimal places they want the output to have.

Code:

#include<stdio.h>
#include<math.h>
#define PI 3.141592654
int main(void) {
//Local Declarations
int x; //desired number of decimal places
float radius; //radius of circle
float circumference; //circumference of circle

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