prefix increment operator does not work as expected

[Hyunho Cho]

GNU Awk 5.0.1, API: 2.0 (GNU MPFR 4.0.2, GNU MP 6.2.0)
 Operating System: Ubuntu 20.04 LTS
 Kernel: Linux 5.4.0-39-generic
 Architecture: x86-64


### 1. "++" prefix increment operator does not work as expected

$ LC_ALL=C awk 'BEGIN { n = 12; x = 2; print n x++ }'           # OK
122

$ LC_ALL=C awk 'BEGIN { n = 12; x = 2; print n ++x }'           # expected 123 
but print 122
122

--------------------------------------------------------------------

$ LC_ALL=C awk 'BEGIN { n = 12; print n x }'                        # OK
12

$ LC_ALL=C awk 'BEGIN { n = 12; print n x++ }'                    # OK
120

$ LC_ALL=C awk 'BEGIN { n = 12; print n ++x }'                    # expected 
121 but print 12
12


### 2. A character in front of "++" operator disappear

$ LC_ALL=C awk 'BEGIN { n = "12,"; print n x }'                  # OK
12,

$ LC_ALL=C awk 'BEGIN { n = "12,"; print n x++ }'              # OK
12,0

$ LC_ALL=C awk 'BEGIN { n = "12,"; print n ++x }'              # expected 12,1 
but print 12
12                                                                              
             # ( "," character disappeared )