foo.cpp: In function 'int main()':
foo.cpp:16:32: error: lvalue required as left operand of assignment
                 p[a[i]]+p[a[j]]=0;
                                ^
foo.cpp:5:31: warning: unused variable 'm' [-Wunused-variable]
 int a[100000],p[100000],z,x=0,m;
                               ^