The variable I and the array a[5] defined in this program are of type int, scanf ("%d ",&; a[I])； The number required in %d is also an integer, so only integer values can be entered. You can change the variable definition type to.

Double I, a [5]; And scanf ("%d ",&; a[I])； Change it to scanf ("%lf ",&; a[I])； You can enter a number with a decimal point.