CODEWITHSUNDEEP
c++cmath
BSchlinker
BSchlinker

Reputation: 3481

Conversion of integer to double

I need to determine the standard deviation of a set of inputs. This requires the summation of (each input - the mean)^2. I have the following code to do this (510 is an example input for testing):

int testDiff = 510;       
console.printf("testDiff = %i \r\n",testDiff);

double testDiff_double = static_cast<double>(testDiff);
console.printf("testDiff_double = %d \r\n",testDiff_double);

double result = pow(static_cast<double>(testDiff),2);
console.printf("result = %d \r\n",result);

However, this code does not generate the expected output (260100). If I print the values obtained at each stage, I get the following:

testDiff = 510
testDiff_double = 0
pow = 0

Why is the conversion from integer to double failing? I am using a static_cast, so I was expecting an error at compile time if there was a logical issue with the conversion.

Note (while it shouldn't matter): I'm running this code on an MBED microcontroller.

Upvotes: 0

Views: 185

Answers (3)

pnezis
pnezis

Reputation: 12321

You have to use %f or %e or %E or %g in order to display a double/float number.

From the printf reference page :

c   Character   
d or i  Signed decimal integer
e   Scientific notation (mantise/exponent) using e character
E   Scientific notation (mantise/exponent) using E character
f   Decimal floating point  
g   Use the shorter of %e or %f
G   Use the shorter of %E or %f
o   Unsigned octal
s   String of characters
u   Unsigned decimal integer
x   Unsigned hexadecimal integer    
X   Unsigned hexadecimal integer (capital letters)
p   Pointer address
n   Nothing printed. The argument must be a pointer to a signed int, where the number of characters written so far is stored.   
%   A % followed by another % character will write % to stdout.

Upvotes: 1

James Leonis
James Leonis

Reputation: 94

In your printf functions, try using %f instead of %d.

Upvotes: 2

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272467

Because you are using %d rather than %f to display the floating-point values.

Upvotes: 2

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