Difference in execution time in C and C++

问题

I recently found this site called codechef, where you can submit solutions to problems. I had submitted two answers for a question, one in C and the other in C++. Both codes are almost the same. But when the code I submitted in C was executed in 4.89s, the code I submitted in C++ was timed out (more than 8 seconds). How is this possible? Where does the time go?

The question was:

Input

The input begins with two positive integers n k (n, k<=107). The next n lines of input contain one positive integer ti, not greater than 10^9, each.

Output

Write a single integer to output, denoting how many integers ti are divisible by k.

Example

Input:
7 3
1
51
966369
7
9
999996
11

Output:
4

My code in C:

 #include<stdio.h>

 int main()  {

   int n,k,t;
   scanf("%d %d",&n,&k);
   int i,num=0;
   for(i=0;i<n;i++)  {
     scanf("%d",&t);
     if(t%k==0)  num++;
   }     

   printf("%d",num);

   return 0;
 }

My Code in C++:

 #include<iostream>

 using namespace std;

 int main()  {

   int n, k, t,num=0;
   cin>>n>>k;
   for(int i=0;i<n;i++)  {
     cin>>t;
     if(t%k==0)  num++;
   }

   cout<<num;
   return 0;
 }

回答1:

The code is not really the same even though they do the same thing

The c++ version uses cin and streams which are slower than scanf etc by default.

By default, cin/cout waste time synchronizing themselves with the C library’s stdio buffers, so that you can freely intermix calls to scanf/printf with operations on cin/cout. You can turn this off with std::ios_base::sync_with_stdio(false);

By doing this the time taken will more or less be similar I would expect

回答2:

I usually add these 3 lines in my code just after the main() for faster input output :

ios_base::sync_with_stdio(false);

cin.tie(NULL);

cout.tie(NULL);

So , Try this :

int main()  
{
   ios_base::sync_with_stdio(false);
   cin.tie(NULL);
   cout.tie(NULL);
   int n, k, t,num=0;
   cin>>n>>k;
   for(int i=0;i<n;i++)  {
     cin>>t;
     if(t%k==0)  num++;
   }

   cout<<num;
   return 0;
 }

来源：https://stackoverflow.com/questions/22225333/difference-in-execution-time-in-c-and-c

标签

c++

executiontimeout