I'm not sure if it's just a browser issue, but this is how your code looks to me:
Obviously that code appears to be missing several things. It may just be a display issue though.
quadratic(double x, double y, double z)
double first, second;
first = (-y+sqrt((y*y)-4*x*z))/(2*x);
second = (-y-sqrt((y*y)-4*x*z))/(2*x);
printf( "%f %f\n", first, second );
double a, b, c;
while( 1 ) //this while loop states that this loop would always run while the operation is true.
printf("Input value a:\n");
scanf( "%f", &a );
if(a>0) printf("input values b and c");
scanf( "\n%f", &b );
scanf( "\n%f", &c );
quadratic( a, b, c );