/in/main.c: In function 'main':
/in/main.c:5:9: error: redefinition of 'A'
     int A=2;
         ^
/in/main.c:4:9: note: previous definition of 'A' was here
     int A=1;
         ^
/in/main.c:6:7: error: 'B' undeclared (first use in this function)
     A+B
       ^
/in/main.c:6:7: note: each undeclared identifier is reported only once for each function it appears in
/in/main.c:7:5: error: expected ';' before 'return'
     return 0;
     ^~~~~~