View Compilation Error

0_0_10263543_26973.cpp: In member function `bigInteger bigInteger::operator+(const bigInteger&) const':
0_0_10263543_26973.cpp:53: error: `i' undeclared (first use this function)
0_0_10263543_26973.cpp:53: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_10263543_26973.cpp: In function `int main()':
0_0_10263543_26973.cpp:86: error: expected `;' before "else"