Miscellany (I do not know how to categorize small point C language.)

1.int a;

printf("%d",2a);

Mathematically speaking, without the slightest problem, but on the computer, it does not recognize!        Correction: should be written as 2 * a.

2. With regard to the output of one decimal place: it should not be written% .lf, but should be written% .1lf!