View Compilation Error

0_0_20437774_18555.cpp: In function 'int main()':
0_0_20437774_18555.cpp:54:30: error: lvalue required as increment operand
    if (flag && (arr[i] == 0) ++ans;
                              ^
0_0_20437774_18555.cpp:54:32: error: expected ')' before 'ans'
    if (flag && (arr[i] == 0) ++ans;
                                ^