[code]
.txt
.globl main

main:

# f= (g+h)-(i+j);

li $s0,0
li $t1,0
li $t2,0
li $s1,4
li $s2,5
li $s3,6
li $s4,7

add $t1, $s1, $s2 # sum of s1,s2 is stored in t1 or temporary variable
t1 contains g+h

add $t2, $s3, $s4 # sum of s3,s4 is stored in t2 or temporary variable
t2 contains i+j

sub $s0, $t1, $t2 # s0 gets $t1- $t2, which is (g+h)-(i+j)
li $v0,1
move $ao, $s0 # suppose to printf("f=%d\n",f)
li $v0, 10
syscall
#it is giving me syntax error
[icode]

You have a problem with the MARS library.

li $v0,1 Print integer
mov $a0,$s0 a0 is integer
syscall <--- MISSING

li $v0,10
syscall #exit

oh thank you but i am still getting syntax error while trying to load on PCSpim as it is saying problem with line where it says .globl main

i meant to say it is not running

here is the code but it is giving me syntax error on function main. Can anyone tell me why please
[code].txt
.globl main

main:
# f= (g+h)-(i+j);

li $s0,0
li $t1,0
li $t2,0
li $s1,4
li $s2,5
li $s3,6
li $s4,7

add $t1, $s1, $s2

add $t2, $s3, $s4

sub $s0, $t1, $t2
li $v0,1
move $a0, $s0
syscall
li $v0, 10
syscall [icode]

I downloaded the PCSPIM simulator and it doesn't like the system calls or the .txt label. I typically use a real MIPS processor, with real tools. Were you instructed to use this simulator, and where did the sample program or the control syntax of your sample program come from? I see no reference to those declarations in PCPSIM's help file!
And no MARS library reference.

Okay, had to get away from it, download and read the Appendix A document, twiddle and retry. It ran. Answer -4.
I also tabbed the text as normally it isn't suppose to be in column 1 but not sure if that was it or not!