c - The value of the output for my double variable is not correct on the Arduino Uno -

i use code test if output displayed correctly when print double variable:

double t = (0.8*0.8*(10^5)*599*(10^-6)*1388.888889)/(287*(25+273)*14.7*3*(10^-3)*4); serial.println(t);  

but output on serial port 4.03 instead of 3.52

i using arduino uno , arduino c language.

what problems code?

how solve problem

in c,c++,javascript,java:

number 10^5 has represented in program 1e5

and number 10^-6 1e-6

the use of '^' forces program perform bit wise operation 10^5 = (10)^(5)

see: https://msdn.microsoft.com/en-us/library/3akey979.aspx

solution

change

double t = (0.8*0.8*(10^5)*599*(10^-6)*1388.888889)/(287*(25+273)*14.7*3*(10^-3)*4); 

to:

double t = (0.8*0.8*(1e5)*599*(1e-6)*1388.888889)/(287*(25+273)*14.7*3*(1e-3)*4); 

now correct result:

t = 3.5292104651726235 

the int on arduino has limited range: 32767 -32768. long 2147483647 -2147483648

avoid mixing int , double avoid rounding error.

use double or can use cast:

 double d = (double)(0.8*0.8*(1e5)*(double)599*(1e-6)*1388.888889)/(((double)287)*((double)(‌​25+273))*((14.7*((double)3)))*(1e-3)*(double)4); 

note on arduino

serial.print(1.23456); //gives "1.23" 

to more numbers convert double variable string , print string.

the example:

double num = (double)(0.8*0.8*(1e5)*(double)599*(1e-6)*1388.888889)/(((double)287)*((double)(25+273))*((14.7*((double)3)))*(1e-3)*(double)4); char output[50];  snprintf(output, 50, "%f", num);  serial.print(output); // should give @ least 3.529210