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Why am I not getting the correct result when calculating the exponent using ^ in C ++?

I am using Bode formuala to calculate the distance of the nth planet from the sun

dist = (4 + 3*(2^(n-2)))/10

If I calculate the distance this way, I get the correct values:

dist[2] = ((4 + 3*1)/10.0) ;  
dist[3] = ((4 + 3*2)/10.0) ;  
dist[4] = ((4 + 3*4)/10.0) ;

But doing it this way gives me wrong values:

vector <double> dist(5);  

for (unsigned int i = 2; i < 5; i++)  
{  
    dist[i] = ((4 + 3*(2^(3-2)))/10.0) ;  
}

Why is that?

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5 answers


The symbol ^

is a bitwise exclusive or, not the exponential function you would expect.

Since you are calculating this in a loop already, you can easily generate the 2 powers you need in the equation, something as simple (and close to your code) would be:



vector<double> dist(5);
unsigned int j = 1;
for(unsigned int i = 2; i < 5; i++){
    dist[i] = (4+3*j)/10.0;
    j = j * 2;
}

In this particular case, we'll initialize the j

first value n-2

you want, then proceed to multiply it by 2 to get the next cardinality of 2 you need.

+8


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Because it is ^

not a force operator in C ++. You can use std::pow

but with double

, or you can do a lot of castings to make it work with int

.



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Primarily:

dist[i] = ((4 + 3*(2^(3-2)))/10.0) ;

Constantly. I assume you wanted to do the following:

dist[i] = ((4 + 3*(pow(2, (i-2)))/10.0) ;
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First, there ^ stands for "xor", not "force". For the other, you compute a constant value (you did 3-2

instead i-2

). However, since you need a power of two, bit shifting might work. ("1 <X" works like "2 ^ X")

vector <double> dist(5);

for (unsigned int i = 2; i < 5; i++) {
   dist[i] = ((4 + 3*(1 << (i - 2)))/10.0) ;
}

For other bases, you need the pow () library function found in <math.h>

/ <cmath>

(C / C ++, respectively).

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Operator ^

in C ++ (and several other languages) means "exclusive" or " not " for more power.

C ++ does not have a "raise force" operator; you need to use a 2-argument function pow

(you can #include

old C-generation <math.h>

or #include <cmath>

and use std::pow

) that returns double

; or as other answers suggested, for this special case you can use bit shift.

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