View Compilation Error

0_0_1971137_1922.cpp: In function `int main()':
0_0_1971137_1922.cpp:10: error: `bignum' undeclared (first use this function)
0_0_1971137_1922.cpp:10: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_1971137_1922.cpp:10: error: expected `;' before "a"
0_0_1971137_1922.cpp:11: error: `a' undeclared (first use this function)