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  1. ///     Raihan Ruhin
  2. ///     CSE, Jahangirnagar University.
  3. ///     Dhaka-Bangladesh.
  4. ///     id: raihanruhin (topcoder / codeforces / codechef / hackerrank), 3235 (lightoj)
  5. ///     mail: raihanruhin@ (yahoo / gmail / facebook)
  6. ///     blog: ruhinraihan.blogspot.com
  7.  
  8. #include<bits/stdc++.h>
  9. using namespace std;
  10.  
  11. #define SET(a) memset(a,-1,sizeof(a))
  12. #define CLR(a) memset(a,0,sizeof(a))
  13. #define PI acos(-1.0)
  14.  
  15. #define MOD 1000000007
  16. #define MX 100010
  17.  
  18. string stringMult(string num1, string num2)
  19. {
  20.     int l1=num1.size(), l2=num2.size();     //length of two arrays.
  21.     int mx=l1+l2;
  22.     int arr[mx];                         //temporary integer array for intermediate calculation.
  23.     CLR(arr);                               //set all value with 0
  24.     int n1[l1], n2[l2];                     //correspondent integer array of two string.
  25.     //ASCII to number
  26.     for(int i=0; i<l1; i++) n1[i]=num1[i]-'0';
  27.     for(int i=0; i<l2; i++) n2[i]=num2[i]-'0';
  28.  
  29.     //calculation
  30.     for(int i=l1-1; i>=0; i--)
  31.         for(int j=l2-1; j>=0; j--)
  32.             arr[i+j+1]+=n1[i]*n2[j];
  33.     //carry
  34.     for(int i=mx-1; i>0; i--)
  35.         if(arr[i]>9)
  36.         {
  37.             arr[i-1]+=arr[i]/10;
  38.             arr[i]=arr[i]%10;
  39.         }
  40.     //eliminate starting zeros.
  41.     int pos=0;
  42.     while(!arr[pos]) pos++;
  43.     //store to a string
  44.     string s="";
  45.     for(int i=pos;i<mx;i++)
  46.         s+=arr[i]+'0';
  47. return s;
  48. }
  49.  
  50. int main()
  51. {
  52.     ios_base::sync_with_stdio(0);
  53.     cin.tie(0);
  54.     int tc,kk=1, n;
  55.     cin>>tc;
  56.  
  57.     while(tc--)
  58.     {
  59.         string a, b;
  60.         cin>>a>>b;
  61.         cout<<"Case "<<kk++<<": "<<stringMult(a, b)<<endl;
  62.     }
  63.     return 0;
  64. }
  65.  
  66.  
Success #stdin #stdout 0s 3436KB
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https://ideone.com/6scQsD
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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