foo.c: In function 'cal':
foo.c:5:5: error: expected '(' before '{' token
     {
     ^
foo.c:6:9: error: unknown type name 'mov'
         mov eax,a;
         ^~~
foo.c:7:9: error: unknown type name 'mov'
         mov ebx,b;
         ^~~
foo.c:8:9: error: unknown type name 'add'
         add eax,ebx;
         ^~~
foo.c:8:13: error: redeclaration of 'eax' with no linkage
         add eax,ebx;
             ^~~
foo.c:6:13: note: previous declaration of 'eax' was here
         mov eax,a;
             ^~~
foo.c:8:17: error: redeclaration of 'ebx' with no linkage
         add eax,ebx;
                 ^~~
foo.c:7:13: note: previous declaration of 'ebx' was here
         mov ebx,b;
             ^~~
foo.c:8:17: warning: unused variable 'ebx' [-Wunused-variable]
         add eax,ebx;
                 ^~~
foo.c:8:13: warning: unused variable 'eax' [-Wunused-variable]
         add eax,ebx;
             ^~~
foo.c:7:17: warning: unused variable 'b' [-Wunused-variable]
         mov ebx,b;
                 ^
foo.c:6:17: warning: unused variable 'a' [-Wunused-variable]
         mov eax,a;
                 ^
foo.c:10:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
foo.c: In function 'main':
foo.c:14:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d",&a,&b);
     ^~~~~~~~~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。