IOSTAT: error status description. Iostat is an integer variable with a default length of 4. When this OPEN statement is executed, the system will assign values to the variables:

Zero, no error occurred.

Negative file end

Positive numbers have errors, and their values depend on specific computer systems.

If this item is omitted, this function is not available.

According to your description, the specified file may not exist. See if your data file 0 1.dat is correct.

In the same directory as the program.