Code:
// ...
#include <stdio.h>
// ...
char buffer[80];
double x = 3.14154;
sprintf( buffer, "%.4f", x );
// buffer == "3.1415"
x = atof( buffer );
// x == 3.1415
double y = 3.14155;
sprintf( buffer, "%.4f", y );
// buffer == "3.1416"
y = atof( buffer );
// y == 3.1416
double z = 3.14156;
sprintf( buffer, "%.4f", z );
// buffer == "3.1416"
z = atof( buffer );
// z == 3.1416
double q = 3.1415;
sprintf( buffer, "%.4f", q );
// buffer == "3.1415"
q = atof( buffer );
// q == 3.1415
double w = 3.141;
sprintf( buffer, "%.4f", w );
// buffer == "3.1410"
w = atof( buffer );
// w == 3.141