The meaning of this error message is that all elements in the array assignment statement must be of the same data type.

The variable A is real(8). Although the assignment in the program is plastic (/ 1, 2,3/), fortran will automatically convert it into real(8).

C=(/ 1, a(2:3)/) In this sentence, 1 is plastic, and the following A (2: 3) is a real number (8), so the data type is different, so the error is reported.

Can be changed to

c=(/ 1.0_8，a(2:3)/)