the power function

[logicode]

Hi, I usualy try to solve class problems on my own but I am hitting a wall.
I am supposed to write a power function and call it in main but having problems like

void power(int base,int exponent)
{
   for( i=0; i<exponent: i++ )
   {
   //This is my trouble area please help. Thanks
 
   }             
}

[sicarie]

Ok, sure. Please use code tags to frame code next time - it helps with readability.

The trick there is to understand what the power function does. So, what does an exponent do, mathematically?

[faceboy]

check this out

code removed per FAQ

[logicode]

ok My apologies. the power function raises the base by the exponent
like x^y
the x is raised to the y power or
x^5 = x*x*x*x*x

[sicarie]

ok My apologies. the power function raises te base by the exponent like x^y
the x is raised to the y power or x^5 = x*x*x*x*x

It's not a big deal, it just helps with readability.

Right, so look at your for loop (specifically, 'exponent') variable, and think about how you could get that functionality.

[sicarie]

Also, how many times does it loop? What do you have to do each single time it loops to get the answer?

[logicode]

It's not a big deal, it just helps with readability.

Right, so look at your for loop (specifically, 'exponent') variable, and think about how you could get that functionality.

i"m stuck..... Can you throw me a hint

[sicarie]

i"m stuck..... Can you throw me a hint

I amended my last post with a reply - see if that helps.

[logicode]

Also, how many times does it loop? What do you have to do each single time it loops to get the answer, and how many times specifically does it loop?

the loop ends when the counter becomes less then the exponent. I was thinking that base=base*base but I knew that wouldnt work so I need a third variable I think to store the original base in and then multiply it by the base untill the loop ends

[faceboy]

faceboy, do not post code again, I have warned you twice, and PM'd you about this.

[sicarie]

the loop ends when the counter becomes less then the exponent. I was thinking that base=base+base but I knew that wouldnt work so I need a third variable I think to store the original base in and then multiply it by the base untill the loop ends

Well, look at your explanation of

x^5 = x*x*x*x*x

This needs to multiply x by x five times, correct?

In c/c++ you can do a nifty little shortcut of

variable += 1 as a shorthand of variable = variable +1

Now let me ask you - if you took x^2 * x^3, what do you get?

[logicode]

Well, look at your explanation of

x^5 = x*x*x*x*x

This needs to multiply x by x five times, correct?

In c/c++ you can do a nifty little shortcut of

variable += 1 as a shorthand of variable = variable +1

Now let me ask you - if you took x^2 * x^3, what do you get?

x^5 and using that method "variable += 1"confuses the crap out of me I rather just use the straight out one.

[sicarie]

x^5 and using that method "variable += 1"confuses the crap out of me I rather just use the straight out one.

That's fine - whatever helps you keep it straight.

Hmm, ok, let's break down the for loop

for (a counter; while the counter is less than 'exponent'; increment the counter)
do something here to get the resulting number

This is the same as
do something here to get the resulting number
do something here to get the resulting number
do something here....
.
.
.
'exponent' number of times.

Is that starting to look something like a possible specific example of x^5 = x*x*x*x*x ?

[logicode]

That's fine - whatever helps you keep it straight.

Hmm, ok, let's break down the for loop

for (a counter; while the counter is less than 'exponent'; increment the counter)
do something here to get the resulting number

This is the same as
do something here to get the resulting number
do something here to get the resulting number
do something here....
.
.
.
'exponent' number of times.

Is that starting to look something like a possible specific example of x^5 = x*x*x*x*x ?

ok...i'm on the edge I know it =] just not quit there

[sicarie]

ok...i'm on the edge I know it =] just not quit there

So you have a loop that will iterate exponent number of times, what action do you want to do one time for each iteration to get the final number?

[logicode]

So you have a loop that will iterate exponent number of times, what action do you want to do one time for each iteration to get the final number?

well you want the base * base so would sum = base * base work I dont think so because then I think the sum with then need to be multiplyed by the base? Am I making things more complex?

[sicarie]

well you want the base * base so would sum = base * base work I dont think so because then I think the sum with then need to be multiplyed by the base? Am I making things more complex?

You are, but you're close. You're right about the base*base. Now think about the fact that you can multiply x^2 by x^3 and get x^5.

Another way of looking at it, x*x = x^2, right? Now let's call that product. What's product * x?

::Edit - I guess product would be more apt than sum, so I updated it.

[logicode]

You are, but you're close. You're right about the base*base. Now think about the fact that you can multiply x^2 by x^3 and get x^5.

Another way of looking at it, x*x = x^2, right? Now let's call that sum. What's sum * x?

x^3 because x^2 * x = x^3

[Ganon11]

You're so close. You're right in thinking that base = base * base; will not work, because with x = 5, your first iteration results in 25, then 625, then...etc.

If you were adding numbers together, you'd use a sum variable. Now, since we are adding, sum should start at 0, because 0 + x = x (This is the Addition Identity Rule). But you are multiplying. If you started sum as 0, then your result would be 0, because 0 * x = 0. What you need is a number n such that n * x = x. Can you think of the number that will fulfill this requirement? This is what your sum variable will start out as - then do sum = sum * base.

[logicode]

You're so close. You're right in thinking that base = base * base; will not work, because with x = 5, your first iteration results in 25, then 625, then...etc.

If you were adding numbers together, you'd use a sum variable. Now, since we are adding, sum should start at 0, because 0 + x = x (This is the Addition Identity Rule). But you are multiplying. If you started sum as 0, then your result would be 0, because 0 * x = 0. What you need is a number n such that n * x = x. Can you think of the number that will fulfill this requirement? This is what your sum variable will start out as - then do sum = sum * base.

well in your example n should start out with sum =1 but doesnt the sum = 1 restart the sum = sum * base when it loops?

[sicarie]

The answer is what you start out with. What are you passed initially?

[logicode]

The answer is what you start out with. What are you passed initially?

I passed in base first and being base

[Ganon11]

well in your example n should start out with sum =1 but doesnt the sum = 1 restart the sum = sum * base when it loops?

OK, think through this example.

I've called the function, passing 5 and 3 (i.e. I want to find 5^3).

Now, sum starts as 1 before the loop.

First execution of the loop: sum = sum * base;
sum = 1 * 5;
sum = 5;

Second execution of the loop: sum = sum * base;
sum = 5 * 5;
sum = 25;

etc...

So, no, using sum = 1 will not reset the value, but setting sum = 0 will.

[sicarie]

I passed in base first and being base

So you start out with base. Can you represent that as an exponent?

[logicode]

So you start out with base. Can you represent that as an exponent?

I dont quite get what you are trying to ask me

[sicarie]

I dont quite get what you are trying to ask me

Look at what Ganon posted, and think about it - you're right there.

[logicode]

OK, think through this example.

I've called the function, passing 5 and 3 (i.e. I want to find 5^3).

Now, sum starts as 1 before the loop.

First execution of the loop: sum = sum * base;
sum = 1 * 5;
sum = 5;

Second execution of the loop: sum = sum * base;
sum = 5 * 5;
sum = 25;

etc...

So, no, using sum = 1 will not reset the value, but setting sum = 0 will.

ok I am seeing the working but I still dont get how you will declare the sum = 1
And in the loop the sum will have a new value but when the loop, loops, I beleive the sum will become 1 again.

[Ganon11]

It would if you declare sum within the loop. But you should declare it right before the loop enters.

[logicode]

hmmm like

for( i=0; i<exponent; i++; sum=1 )
{
sum= base* sum
}

then base which is the base will be multiplyed by the sum which os one but when the loop comes back around wont the sum be 1 again? This doesnt make sense to me.

[Ganon11]

No, since you are assigning the new value (sum * base) to sum, it will change values every time within the loop. Try it for yourself to see that it changes.

[sicarie]

Try declaring sum right before your for loop.

[logicode]

Try declaring sum right before your for loop.

I get one error when I try to run it says parse error and points to
for (int i = 0; i < exp; i++; )

[sicarie]

I get one error when I try to run it says parse error and points to

for (int i = 0; i < exp; i++;);

Just a slight syntax error - try removing the semi-colon from the right side of the for loop.

[logicode]

Just a slight syntax error - try removing the semi-colon from the right side of the for loop.

ahh ok I dont know why but that works so here is the thing
I input 5
then input 2
it says that the answer is 5
cout<<sum

[sicarie]

ahh ok I dont know why but that works so here is the thing
I input 5
then input 2
it says that the answer is 5
cout<<sum

And your main follows pseudocode of:

declare vars
get input
call function
save function return value
print function return value

?

[logicode]

can I send in my code so you can see it

[logicode]

  for (int i = 0; i < exp; i++);
  {
    sum= base*sum;
     return sum;
   }
 

[sicarie]

Your return statement - you have it inside your for loop. This means you return on the first execution of the loop. You want to return when the loop is completed.

[logicode]

  for (int i = 0; i < exp; i++);
{
    sum= base*sum;
}
      return sum;
 
}

ok I should have seen that but in this one All I get in return is the origional value

[sicarie]

  for (int i = 0; i < exp; i++);
 

You still have a ';' after your for loop, remove that. For statements are a little weird in that they are not terminated by a semicolon, but the stuff inside them still is.

doStuff();
for (part1; part1; part3) {             // no ';' here
    initialize.someVariable();        // ended with a semicolon
}                                              // no ';' here either
doStuff(with.someVariable());     // ended with a semicolon
 

[Michael Safyan]

Before I begin...

• Readers looking for Power C++ can find it at the link.
• Readers interested in the builtin C++ power function should include <cmath> and execute "std::pow".

To answer the question...

Code removed - please read posting guidelines.