I making a program which runs a "greedy" algorithm — one which asks for an input value of change owed and returns the minimum amount of coins required to return that change while using as few coins as possible. The only coins which can be used are the quarter, dime, nickel and penny. Please take a look at my code and tell me how I could fix the error being displayed.

```
#include <stdio.h>
#include <cs50.h>
#include <math.h>

int main(void)
{
    float change;
    int counter;
    counter = 0;
    do 
    {
        printf("Please imput how much change is owed: ");
        change = GetFloat();
    }
    while (change<=0); 
    int centv;
    {
        centv = round(change*100);
    }

    int quarter, dime, nickel, penny;
    quarter= 25;
    dime= 10;
    nickel= 5;
    penny= 1;

    {
        while( centv>=quarter )
            {       
                (centv-25);
                counter++;  
            }

        while( centv>=dime )  
            {                
                (centv-10);
                counter++;
            }        
        while( centv>=nickel )
            {            
                (centv-5);
                counter++;
            }
        while( centv>=penny)
            {
                (centv-1);
                counter++;
            }   

        if(centv == 0)
            {
                printf("%i \n", counter);
            }
    }
}

```

The errors I'm getting are with the lines `(centv-25)`, `(centv-10)`, `(centv-5)` and `(cent-1)`. 

The error message is "expression result unused" for all of them.
How do I fix this?