/in/foo.cc: In function 'int main()':
/in/foo.cc:14:6: warning: statement has no effect [-Wunused-value]
 for(A;A<=i;A++)
      ^
/in/foo.cc:22:6: warning: statement has no effect [-Wunused-value]
 for(B;B<=j;B++)
      ^
/in/foo.cc:6:5: warning: unused variable 'a1' [-Wunused-variable]
 int a1,a2,b1,b2,s1=0,s2=0,i,j,n,A=1,B=1,x=0;
     ^~
/in/foo.cc:6:8: warning: unused variable 'a2' [-Wunused-variable]
 int a1,a2,b1,b2,s1=0,s2=0,i,j,n,A=1,B=1,x=0;
        ^~