Caught in a loop for some reason...

[iflash]

Hi, i am new to C and when i tested my little program there comes an infinite loooooop. I searched for bugs but couldn't find any, pls help out. Source code is here:

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/* Calculates total earnings of salesman per week. */

#include <stdio.h>

int main()
{
float sales, commission;
int retainer = 200;

printf( "Enter sales in dollars (-1 to end): " );
scanf( "%.2f", &sales );

while ( sales != -1 ) {
commission = sales * 9 / 100;
printf( "\nSalary is: %.2f\n", commission + retainer );

printf( "Enter sales in dollars (-1 to end): " );
scanf( "%.2f", &sales );
}

return 0;

}

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The output of the program on my screen is attached in a .jpg file. Pls read and thnx in advance. Just pls find out whats wrong with this piece of code.