View Compilation Error

0_0_26685466_8609.cpp: In function 'int main()':
0_0_26685466_8609.cpp:16:13: error: 'a' was not declared in this scope
             a[x[i]][y[i]]=1;
             ^
0_0_26685466_8609.cpp:24:25: error: 'a' was not declared in this scope
                     if(!a[tx][ty]){
                         ^
0_0_26685466_8609.cpp:39:13: error: 'a' was not declared in this scope
             a[x[i]][y[i]]=0;
             ^