How to print a variable and set its value without casting its type

been using gas assembler and here is code below that moves a data between register and memory

  3 .section .data
  4     constant:
  5         .int 10
  6 
  7 .section .text
  8     .globl _start
  9 
 10 _start:
 11     nop
 12 
 13 mov_immediate_data_between_reg_and_mem:
 14     movl $777, %eax
 15     movl %eax, constant
 16 
 17 exit:
 18     movl $1, %eax
 19     movl $0, %ebx
 20     int $0x80

then created executable file and linker and then i debug that code below, i want to to print a changed value of variable and then error appears:

Breakpoint 1, 0x08049000 in _start ()
(gdb) si
0x08049001 in mov_immediate_data_between_reg_and_mem ()
(gdb) si
0x08049006 in mov_immediate_data_between_reg_and_mem ()
(gdb) si
0x0804900b in exit ()
(gdb) print constant
'constant' has unknown type; cast it to its declared type

but when i cast it with its type it works perfect:

(gdb) print (int)constant
$1 = 777

and if i try to assign new value to a variable it push the same error and if i try to set a new value to variable with its type it push the error below:

(gdb) set (int)constant = 666
Left operand of assignment is not an lvalue.