Google is your friend:
For example, if your program has a variable width, you get an error if you try to set a new value with just `set width=13', because GDB has the command set width:
(gdb) whatis width
type = double
(gdb) p width $4 = 13
(gdb) set width=47
Invalid syntax in expression.
(gdb) whatis width
type = double
(gdb) p width $4 = 13
(gdb) set width=47
Invalid syntax in expression.
The invalid expression, of course, is `=47'. In order to actually set the program's variable width, use
(gdb) set var width=47
(gdb) set var width=47
You can find the needed information in the following document:
