Difference between sap abap programming SY-REPID and SY-CPROG

First, it is interpreted as sy-repid is the name of the current program. "the program name of the current program
Sy-cprog is the name of the calling program. "Name of the program called

Write a simple program and tune the FM program. You will know the difference. When the program enters the FM

Sy-repid is the name of the functionpool where the FM is located,
Sy-cprog is the program name that calls this FM report.

Also, the SY-REPID cannot be changed, and the SY-CPROG can be modified just like other data structures.

Difference between sap abap programming SY-REPID and SY-CPROG