View Compilation Error

0_0_32907193_13966.cpp: In function 'int main()':
0_0_32907193_13966.cpp:23:22: error: 'flag' was not declared in this scope
    if(a[i]==-1) a[i]=flag;
                      ^
0_0_32907193_13966.cpp:24:9: error: 'flag' was not declared in this scope
    else flag=a[i];
         ^