A very Basic doubt in C operators

Question

0.00/5 (No votes)

See more:

#include<stdio.h>
int main()
{
       float sum;
       sum=0; 
     
       for(int n=1; n<=10; ++n)
       {
          sum=sum+1/float(n);  
         printf("%f",sum);
       }

}

The program here calculates 1/1+1/2+1/3+1/4+.......+1/n
My question here is on the for loop increment . What difference is there between ++n and n++ prior to this program.
I know it's pre and post increment....But to this program how does it work??

Posted 10-Apr-13 16:26pm

Nirmal77

Updated 10-Apr-13 16:37pm

PIEBALDconsult

v3

Add a Solution

3 solutions

Solution 2

++n; is more efficient,n++ ; in Compilar n++ is more than ++n one step

Posted 11-Apr-13 22:54pm

xujingrzx

Comments

CPallini 12-Apr-13 5:01am

In such a simple case, the compiler might easily optimize.

Solution 3

You can check the difference in this code

void main()
{
int n;
int x,y;
n=1;
printf("Initial Value = %d",n);
x=n++;
printf("Assigned %d and Incremented %d",x,n);
y=++n;
printf("Assigned %d and Incremented %d",y,n);
}

Posted 15-May-13 0:49am

vinotamil

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

PIEBALDconsult · Accepted Answer · 2013-04-10T16:39:00

Solution 1

They are equivalent, in this usage; most practitioners use post-increment, some insist that pre-increment is more efficient.

Posted 10-Apr-13 16:39pm

PIEBALDconsult

Comments

Sergey Alexandrovich Kryukov 11-Apr-13 0:20am

This is amazing, but I tested pre-increment with .NET, it really improves performance by clearly noticeable percentage.
My 5 anyway.
—SA

PIEBALDconsult 11-Apr-13 0:35am

Write an article.

Sergey Alexandrovich Kryukov 11-Apr-13 0:40am

Thank you. Nah.., there are more interesting topics; I have some line of unfinished articles...
—SA

Steve44 12-Apr-13 5:50am

Pretty basic, the post-increment creates a temporary variable containing the value before incrementing the original variable and returns this as the value of the operation. This is most noticeable when you are overloading increment operators on a class object, there pre-increment increments the instance in-place, while post-increment creates a copy of the instance. For C the difference is minimal.

H.Brydon 12-Apr-13 12:40pm

Differences in pre- and post- increment (also decrement) will be seen in either (1) unoptimized int code, (2) code involving a class/struct that acts like an int and (3) use of operator++()/operator--(). In all cases, the value has to be preserved for the postincrement (or postdecrement) return value. In the case of POD, the compiler can optimize this out. For a class this is a harder problem and is not always optimized out (if ever?). For the third case it can't be optimized.

Sergey Alexandrovich Kryukov 12-Apr-13 15:29pm

I could understand it, but I observed what I observed in a particular case of simplest possible .NET code. I did not look at disassembled code though...
—SA

H.Brydon 12-Apr-13 15:36pm

Okay. I also suspect that .NET will give different answers from C++, which will give "more" answers than POD with C, and OP's question was "C" based.

CPallini 12-Apr-13 4:59am

There is a reason why pre-increment is more efficient. More noticeable on C++ than in C, however.

Sergey Alexandrovich Kryukov 12-Apr-13 15:31pm

This is interesting and not obvious to me. I observed that on .NET loop in the simplest possible case (please see discussion above), but did not find out why.
—SA

CPallini 12-Apr-13 16:30pm

See here (point 3 of the solution): http://www.gotw.ca/gotw/002.htm
(It has already pointed out by Steve44 and H.Brydon).

Sergey Alexandrovich Kryukov 12-Apr-13 16:34pm

Aha, makes sense, thank you.
—SA