PE 25 1000-digit Fibonacci number

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#include <iostream>#include <list>typedef char Digit;class BigInt{public:BigInt () { };BigInt (unsigned int i);BigInt (const char* i);BigInt operator+ (const BigInt& big);int size() const { return number.size(); }private:std::list<Digit> number;};BigInt::BigInt (unsigned int i){    while (i) { number.push_front (i % 10); i/=10; }}BigInt::BigInt (const char* i){    for(const char* it=i;*it != 0; it++)number.push_back(*it-'0');}BigIntBigInt::operator+ (const BigInt& big){    char carry = 0;    char tmp;    BigInt result;    std::list<Digit>::reverse_iterator it;    std::list<Digit>::const_reverse_iterator it2;    for (it = number.rbegin(), it2 = big.number.rbegin();it != number.rend() || it2 != big.number.rend();it != number.rend() ? it++ : it, it2 != big.number.rend() ? it2++ : it2)    {        tmp = (it != number.rend() ? *it:0) +(it2 != big.number.rend() ? *it2:0) +carry;        if (tmp > 9)        {            tmp = tmp - 10;            carry = 1;        }        else        {            carry = 0;        }        result.number.push_front(tmp);    }    if (carry) result.number.push_front(1);    return result;}int main(void){    BigInt prev2 = 1;    BigInt prev1 = 1;    BigInt current = prev1 + prev2;    int term = 3;    while (current.size() != 1000)    {        term++;        prev2 = prev1;        prev1 = current;        current = prev1 + prev2;    }    std::cout << "Solution:" << term << std::endl;return 0;}
Answer:
4782
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