50.0D 16 means that 50.0 of 10 is multiplied by the power of 16, which is double precision. \x0d\ To put it bluntly, it means double precision 50.0E 16\x0d\ and others are similar. \x0d\ Pay special attention to the accuracy of constants. \x0d\ if double a, b \ x0d \ a = 3.141592654323213 \ x0d \ if b = a * 7.0\x0d\, the accuracy may be lost, because although a is. \x0d\ To ensure the accuracy of b = a * 7.0, 7.0 should be written as 7.0D0.