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multiply using << several times

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multiply using << several times

 
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  #1
May 26th, 2009
the question reads as follows....

show how u can efficiently multiply an integer that is read from the keyboard by 100, without using the operator *. use the << operator several times....

ok i can do this using overload.... or thats the only way i can think of... or is it actually possible to use << to muliply the number.


my code so far... (just to get the number)


C++ Syntax (Toggle Plain Text) 
  1. #include <iostream>
  2. #include <stdlib.h>
  3.  
  4. using namespace std;
  5.  
  6. int num;
  7.  
  8. int main(int argc, char *argv[])
  9. {
  10.   cout << "Enter a number from: ";
  11.   cin >> num;
  12.  
  13.   system("PAUSE");	
  14.   return 0;
  15. }

oh and thanx
Last edited by phoenix911; May 26th, 2009 at 10:25 am. Reason: 4got to say thanx :/
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Re: multiply using << several times

 
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  #2
May 26th, 2009
im not thinking at all.... all i can do is say

C++ Syntax (Toggle Plain Text) 
  1.  
  2. cout << num << "00";

or is there a way to multiply with <<??
Last edited by phoenix911; May 26th, 2009 at 10:27 am. Reason: was a bit slow
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Re: multiply using << several times

 
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  #3
May 26th, 2009
Use the shift operators.

http://www.learncpp.com/cpp-tutorial...ise-operators/

Multiplying by a factor of 2 is much easier than multiplying by 100. Here's a basic example of how to use shift operators.

C++ Syntax (Toggle Plain Text) 
  1. #include <iostream>
  2. using namespace std;
  3.  
  4. int main ()
  5. {
  6.     int a = 12; // a = 12
  7.     cout << a << endl;
  8.     a = a >> 1; // a = 12 / 2 = 6
  9.     cout << a << endl;
  10.     a = a << 3; // a = 6 * 8 = 48
  11.     cout << a << endl;
  12.     cin.get ();
  13.     return 0;
  14. }
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Re: multiply using << several times

 
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  #4
May 26th, 2009
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Originally Posted by phoenix911 View Post
im not thinking at all.... all i can do is say

C++ Syntax (Toggle Plain Text) 
  1.  
  2. cout << num << "00";

or is there a way to multiply with <<??
haha, that's thinking outside the box. Yeah, that'll work for "multiplying" by 100 but if you want to change the multiplier to 5 then you're boned. This made me laugh pretty hard.
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Re: multiply using << several times

 
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  #5
May 26th, 2009
use the additive property:

(a * m) + (a * n) = a * (m + n)

example:
cpp Syntax (Toggle Plain Text) 
  1. result = (a << 2) + (a << 4);  
  2. // result now contains the sum,  4a + 16a = 20a
  3.  
  4. cout << a << " times 20 = " << result << endl;


.
Last edited by jephthah; May 26th, 2009 at 3:42 pm.
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Re: multiply using << several times

 
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  #6
May 26th, 2009
er.. i mean "distributive property"

thanks Dave
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Re: multiply using << several times

 
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  #7
May 27th, 2009
are you allowed to just divide by .01

C++ Syntax (Toggle Plain Text) 
  1. int num;
  2. cin>>num;
  3. int answer / .01;
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Re: multiply using << several times

 
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  #8
May 27th, 2009
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Originally Posted by jloundy View Post
are you allowed to just divide by .01

int num;
cin>>num;
int answer / .01;  // huh?
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Originally Posted by phoenix911 View Post
the question reads as follows....

show how u can efficiently multiply an integer that is read from the keyboard by 100, without using the operator *. use the << operator several times....
The << operator is required. What happened to the OP anyway?
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Re: multiply using << several times

 
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  #9
May 27th, 2009
i meant int answer = num/.01;
same thing as multiplying by 100,
but i guess u have to use << so im wrong again
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Re: multiply using << several times

 
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  #10
May 28th, 2009
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Originally Posted by jloundy View Post
i meant int answer = num/.01;
same thing as multiplying by 100,
but i guess u have to use << so im wrong again
that's not the only reason why you're wrong.

mainly you're wrong because you can't divide an int by a float and expect to get a correct integer result.

go on try it. you might actually learn something.


.
Last edited by jephthah; May 28th, 2009 at 11:43 am.
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