Problem with sine function :(

I can use sine function, but I wanted the Program to display the number without zeros like 0.500000, it works for all number (including 0.5) except sin, cos, and tan answers, I don't get the answer and a loop seems to be unclosed..can anyone help?
x,y,z, deci_test are double
deci_chk, deci_cnt, q are int

Code:

                        z=x*sin(y*(3.14159265/180));
                        deci_test=z;
			q=0;
			deci_cnt=0;
			while (q==0)
			{
				deci_chk=deci_test;
				if (deci_test==deci_chk)
					q=1;
				else 
				{
					deci_test=deci_test*10;
					deci_cnt++;
				}
			}
			if (deci_cnt==0)
				printf("%.0f",z);
			else if (deci_cnt==1)
				printf("%.1f",z);
			else if (deci_cnt==2)
				printf("%.2f",z);
			else if (deci_cnt==3)
				printf("%.3f",z);
			else if (deci_cnt==4)
				printf("%.4f",z);
			else if (deci_cnt==5)
				printf("%.5f",z);
			else
				printf("%f",z);

if the input is 0.500000 the out put is 0.5
but if the input is sin(30) the program doesn't display any output and a loop seems to be unclosed.. :-S

Why not just use "%g"?

sorry I'm still a small beginner, can you explain a little?

printf(3): formatted output conversion - Linux man page

omg that's much much better )))))))))
Thanks pretty much that helped aloooot