power function in c programming

Question

1.00/5 (1 vote)

See more:

XML

#include<stdio.h>
#include<math.h>
int main()
{
    int a=2,c;
    c=pow(++a,a++);
    printf("%d",c);
}

output is 16

Posted 11-Jan-14 16:50pm

Sunil Kumar Das

Updated 11-Jan-14 16:51pm

v2

Add a Solution

Comments

Ron Beyer 11-Jan-14 23:03pm

And the question is?

3 solutions

Solution 3

Evaluation of function call parameters is "unsequenced" according to the language specification.
Side effects (like pre-/post- -increment/-decrement) on multiple arguments is therefore "undefined behaviour".

I.e. a compiler is free to evaluate function arguments in any order before executing the function body - no guarantee that it is evaluated from left to right, nor from right to left, nor any other sequence.

The only solution to this: don't do (multiple) side effects on the same object in one full expression.

E.g. the following are also undefined behaviour:

C++

int  a = ...
int *b = ...
a = b[a++];  // undefined behaviour
a = a++ + 1; // undefined behaviour

The language specification has several "undefined behaviour". Undefined behaviour is: "behavior for which this International Standard imposes no requirements".

Cheers
Andi

Posted 12-Jan-14 1:00am

Andreas Gieriet

Comments

[no name] 12-Jan-14 19:51pm

I think it is good that you have reminded us of this.

Andreas Gieriet 13-Jan-14 7:37am

Not everything that is possible should also be done.
It's better to know when leaving secure paths and venturing onto thin ice ;-)
Cheers
Andi

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)

User 59241 · Accepted Answer · 2014-01-11T17:43:00

If you read this you will see how function parameters are commonly pushed onto the stack starting from the right hand side.

http://www.csee.umbc.edu/~chang/cs313.s02/stack.shtml[^]

It appears you compiler uses this convention as do ms c compilers

For pow(x,y) y would be pushed first then x.

Now in your function call the rightmost expression is a++ (postfix) so the value of a == 2 is pushed first then incremented.
The variable a now has the value 3.
The next expression is ++a so a is incremented again making it 4 and the value is then pushed on the stack.

Thus for the function call to pow the stack now holds the value of 2 for y and 4 for x.

4^2=16.

Ron Beyer · Accepted Answer · 2014-01-11T17:20:00

If you are wondering why its 16 and not 27, here's why:

First, it pushes a++ on the function stack, which pushes 2.
Then it post-increments a++ turning it into 3.
Then it pre-increments a++ turning it into 4.
Then it pushes 4 onto the stack.

4 raised to the power of 2 (squared) is 16.

Oddly enough, in .NET, this gives you a value of 27, because in .NET it behaves a little differently. First it pre-increments a turning it into 3, pushes 3 onto the stack then increments it to 4, then the equation becomes 4 cubed or 27.

power function in c programming

3 solutions

Solution 2

Solution 3

Solution 1

Add your solution here

Preview 0