Just include std::ios::sync_with_stdio(false); in your code, and cin will be as fast as scanf.

Like mukel said, ios_base::sync_with_stdio(0) makes c++ io streams' performance comparable to cstdio's. Have a look at the following thread: http://codeforces.net/blog/entry/925, as well as here: The Standard Librarian: IOStreams and Stdio.

Once, at another Online Judge, I kept getting TLE's for an algorithm that was quite IO intensive. I was using cin/cout and ios_base::sync_with_stdio(0) as the first line of main()'s body. I switched back to scanf/printf and got AC. Depends on the implementation. To me, it works wonderfully at CodeForces.

PD:Also, favor '\n' instead of endl for ending lines. endl flushes the buffer every time.

but also notice: with std::ios::sync_with_stdio(false);, don't mix C-style IO (scanf/printf, gets/puts, getchar/putchar ... ) with C++-style IO (cin/cout ... ), since cin/cout is not sync with stdio, you may get same data from using scanf and then use cin again.

You might find this post of mine useful: http://codeforces.net/blog/entry/5217

Untie of stream may also help http://www.cplusplus.com/reference/ios/ios/tie/

Put this: ios_base::sync_with_stdio(false);cin.tie(0); in the beggining of the main func. cin/cout will be as fast as scanf and printf (even faster). BUT DONT USE ENDL (use "\n")

I use stringstream to store output first and output it on the last line as cout << ss.str();.

This works great when you input and output alternatively. (For example, when you output as you answer query)

fastest I is getchar_unlocked()

I use this recently, and work very good :

using namespace std;

typedef long long i64;

const int MAX_STRING_LENGTH = 1;
#define endl  "\n"

struct _io{
  char buff[MAX_STRING_LENGTH];

  _io & operator >>(int &x){
    scanf("%d",&x);
    return *this;
  }
  _io & operator >>(i64 &x){
    scanf("%I64d",&x);
    return *this;
  }
  _io & operator >>(float &x){
    scanf("%f",&x);
    return *this;
  }
  _io & operator >>(double &x){
    scanf("%lf",&x);
    return *this;
  }
  _io & operator >>(long double &x){
    scanf("%llf",&x);
    return *this;
  }

  _io & operator >>(char &c){
    scanf("%c",&c);
    return *this;
  }

  _io & operator >>( char *s ){
    scanf("%s",s);
    return *this;
  }

  _io & operator >>( string &s ){
    scanf("%s",buff);
    s = string(buff,strlen(buff));
    return *this;
  }
  _io & operator <<(int x){
    printf("%d",x);
    return *this;
  }

  _io & operator <<(i64 x){
    printf("%I64d",x);
    return *this;
  }

  _io & operator <<(float x){
    printf("%f",x);
    return *this;
  }

  _io & operator <<(double &x){
    printf("%lf",x);
    return *this;
  }

  _io & operator <<(long double &x){
    printf("%llf",x);
    return *this;
  }

  _io operator <<(char &c){
    printf("%c",c);
    return *this;
  }

  _io & operator <<( string &s ){
    printf("%s",s.c_str());
    return *this;
  }

  _io & operator <<( char *s ){
    printf("%s",s);
    return *this;
  }
}io;

int main(){
int a, b; 
io>>a>>b;
io<<(a+b)<<endl;
}

Hey guys, thanks for such an excellent discussion. I've read the entire page, but forgive me if I missed something, as I am going to ask a stupid question. * What if sometimes I want to use cin cout and sometimes printf, scanf etc. in the same code ? I mean, can I switch ON / OFF std::ios::sync_with_stdio(); whenever I want ?

I don't like tradeoffs, so I ended up writing my own version http://codeforces.net/blog/entry/45835

Before few minutes, I have solved Light oj problem no: 1087,problem title: "Diablo". In that problem, at first, I have used cin/count along with ios_base::sync_with_stdio(false);cin.tie(0);. I have also used #define endl "\n" and used no printf/scanf, which gave me Runtime Error. Later on, I have given up only this part cin.tie(0); and everything was similar like the before which gave me Time Limit Exceed. At last, I have used only printf/scanf which gave me Accepted.

Can any body explain it? (Thanks In Advance)