C++实现大数乘法算法代码
//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; }
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