//大数乘法算法 #include<iostream> #include<string> #include<cstring> using namespace std; int main() {     string num1,num2;     cin >> num1 >> num2;     //cout << num1.size() << " " << num2.size() << endl;     const char* n1;     const char* n2;     if (num1.size() < num2.size())     {         n1 = num2.c_str();         n2 = num1.c_str();     }     else     {         n1 = num1.c_str();         n2 = num2.c_str();     }     char* n = new char[strlen(n1)+strlen(n2)+1];     for (unsigned int i = 0; i < strlen(n1)+strlen(n2); i++)         n[i] = '0';     n[strlen(n1)+strlen(n2)]='\0';     //cout << strlen(n) << endl;     int count = 0,flag = 0;     for (int i = strlen(n1)-1; i >= 0; i--)     {         flag++;         int x1 = n1[i]-'0';         //cout << "n1["<< i << "]为：" << x1 << endl;         char carry = '0';         for (int j = strlen(n2)-1; j >= 0; j--)         {             int x2 = n2[j]-'0';             //cout << "n2["<< j << "]为：" << x2 << endl;             //cout << "当前位未改变前值为: " << n[count] << endl;             int sum = x1*x2 + (carry-'0') + n[count]-'0';             //cout << "sum is " << sum << endl;             n[count++] = (sum % 10)+'0';             carry = (sum / 10)+'0';             //cout << "当前位的值为: " << n[count-1] << endl;             //cout << "carry的值为：" << carry << endl;         }         if (carry != '0')         {             n[count] = carry;             count = flag;             //cout << "当前位的值为: " << n[count] << endl;         }         else             count = flag;     }     for (int i = strlen(n)-1; i >= 0; i--)     {         if ((i == strlen(n)-1)&&(n[i] == '0'))             continue;         cout << n[i];     }     cout << endl;     delete[]n;     system("pause");     return 0; }