I stands for integer and a stands for string. In your question, 20A should be changed to A20, and the numbers after I and A represent the finite length of integers and strings.

This shows that myid is a two-digit integer, numprocs is a one-digit integer, and processor_name is a string of no more than 20 characters. Before this output statement, all three variables will be assigned values.

Write (*, 10) here, 10 represents the output format, and there is a limited 10 format ('hello world! Process', I2,' of', I 1,' on', A20).

The method here is the simplest.