1381. a*b

#include <iostream>
#include <cstdlib> 
#include <string>
using namespace std;

string clear(string s){     
      if(s.length()==0)
           s = "0";
      while(s.length()>0 && s[0]=='0'){             
           //重点1.使用该函数来删除不要的子串，千万不要使用以下错误做法
          /*for(int i=0;i<s.length();i++){
              s[i]=s[i+1]; 
          } 该程序运行后，s.length()是不变的，但是所有值都变成'\0';*/  
           s.erase(0,1);             
      }       
      if(s.length()==0) 
           s = "0";  //s = '0';
      return s; 
} 

string addition(string s1,string s2){
      
      while(s1.length()<s2.length()){
           s1 = '0' +s1;
      }
      
      while(s1.length()>s2.length()){
           s2 = '0' +s2;
      }
      
      s1 = '0' + s1;
      s2 = '0' + s2;
      /* 重点2：以后使用i--的时候切记for第二个条件是符合条件，i<0是错误的！ 
      for(int i = s1.length()-1;i<0;i--){
          s1[i] = s1[i] + (s2[i]-'0');
          if(s1[i]>'9'){
             s1[i] = s1[i] - 10;
             s1[i-1] = s1[i-1] + 1;              
          } 
      } */
      for(int i = s1.length()-1;0<=i;i--){
          s1[i] = s1[i] + (s2[i]-'0');
          if(s1[i]>'9'){
             s1[i] = s1[i] - 10;
             s1[i-1] = s1[i-1] + 1;              
          } 
      }  
      s1 = clear(s1);
      return s1; 
}


string multiply(string s1,string s2){
       string result;
       result = "0";
       //重点3：if语句如果遇到多语句，务必记得加上{} 
	   if(clear(s1) =="0" || clear(s2) =="0")
       return result ;
       for(int i=s2.length()-1;0<=i;i--){
          for(char c='1';c<=s2[i];c++){
              result = addition(result,s1); 
          } 
          s1 = s1 + '0'; 
       } 
       result = clear(result);
       return result;       

}

int main(){
   
   //重点4:以后输入样例时不需要全部输入再输出！     
   /*int T;
   string s1[100000];
   string s2[100000]; 
   cin >> T; 
   for(int i=0;i<T;i++){
      cin >> s1[i];
      cin >> s2[i];     
   } 
   for(int i=0;i<T;i++){
      cout << multiply(s1[i],s2[i])<<endl; 
   }*/
   
   int T;
   string s1;
   string s2;
   string result; 
   cin >> T; 
   for(int i=0;i<T;i++){
      cin >> s1;
      cin >> s2; 
      result = multiply(s1,s2);
      cout <<  result <<endl;     
   } 
   //system("pause"); 
   return 0;
}