View Compilation Error

0_0_30293052_5137.cpp: In function 'int main()':
0_0_30293052_5137.cpp:50:19: error: 'stu' was not declared in this scope
             cout<<stu[i].a<<"+"<<stu[i].b<<"="<<"["<<stu[i].ch<<stu[i].res<<"]"<<endl;
                   ^