View Compilation Error

0_0_18852189_22667.cpp:52:10: error: variable or field 'add' declared void
 void add(Bignum &a,Bignum &b)
          ^
0_0_18852189_22667.cpp:52:10: error: 'Bignum' was not declared in this scope
0_0_18852189_22667.cpp:52:20: error: 'Bignum' was not declared in this scope
 void add(Bignum &a,Bignum &b)
                    ^
0_0_18852189_22667.cpp:52:28: error: 'b' was not declared in this scope
 void add(Bignum &a,Bignum &b)
                            ^