how do i make a function that takes 2 numbers as arguments (1 as the
number and the 2nd as
the exponent) and raises that number to the power (stored as exponent)
i worked this out.. though i could not get the logical statement inside
the for-loop right.
it's squaring itself for every one incrementation!
here's the listing:

double long pwr( double long num,int exp)
{
int y = 0;
for( y = 1;y <= exp; y++)
{
num = num*num;
}
return num;
}

"MC Felon" <paec.nwa@gmail.com> writes:


Let's add some assertions to understand what it is computing:


/* num = n = n^(2^y) */


/* num = n^(2^(y-1)) */


/* num = n^(2^y) */


/* num = n^(2^exp) */


So your function pwr(n,e) returns n^(2^e).


Now what you want is n^e.
What does this mean?

n^e = n*n*n*....*n
\_____...._/
e times n

n^e = n*(n*n*....*n
\___...._/
e-1 times n

n^e = n*(n^(e-1))

Another interesting factoid is that n^0 = 1

Therefore we could take as invariant assertion: p = n^i

/* p = n^(i-1) */
p*=n;
/* p = n*n^(i-1) = n^i */

Now, if we add as stop condition i==e, we'd get as post condition:

/* p = n^i & i = e */ ==> /* p = n^e */

which is what we want. So:

while(i!=e){
/* p = n^i) */
i++;
/* p = n^(i-1) */
p*=n;
/* p = n^i) */
}
/* p = n^e */


Remains to add the initial condition: /* i = 0 & p = n^0 */
To ensure that, we need to execute: i=0; p=1;

int pwr(unsigned int n,unsigned int e){
unsigned int i;
unsigned int p;

i=0;p=1;
/* i = 0 & p = n^0 */
while(i!=e){
/* p = n^i) */
i++;
/* p = n^(i-1) */
p*=n;
/* p = n^i) */
}
/* p = n^e */

return p;
}


--
__Pascal Bourguignon__ http://www.informatimago.com/

PLEASE NOTE: Some quantum physics theories suggest that when the
consumer is not directly observing this product, it may cease to
exist or will exist only in a vague and undetermined state.

Pascal Bourguignon wrote:


THANKS A LOT!!!!!
i am not finding words to thank u....
regards!
will ask here if i have doubts!