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array to long conversion

 
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ashrafkhatri



Joined: 06 May 2008
Posts: 14

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array to long conversion
PostPosted: Mon Feb 27, 2017 1:37 am     Reply with quote

Hi;

I am getting currect data from serial port and i save it in array of 3.
i.e:
int array_display[3];

now i want to convert it to long int.
array_display[0] will be save on unit place of long int
array_display[1] will be save on ten place of long int &
array_display[2] will be save on hundred place of long int

Example:
if array_display[0] = 3 , array_display[1] = 4 & array_display[2] = 5 then
long int new_data should be 543.

& i used the following formula but it is not working.
new_data = array_display[0] + array_display[1]*10 + array_display[2]*100;

what is wrong with the method. Any Idea?
Ttelmah



Joined: 11 Mar 2010
Posts: 19538

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PostPosted: Mon Feb 27, 2017 1:58 am     Reply with quote

Critical change:

new_data = array_display[0] + array_display[1]*10 + array_display[2]*100L;

Note the 'L'.

Problem is that each 'array_display' value is an int8. '100' is also an int8. 5*100 using int8 maths, overflows and gives you 244.

Only the 'hundreds' can overflow this way (9*10 = 90 is still small enough to fit in an int8). Adding the 'L' makes the constant '100', into a 'long' (int16). So int16 arithmetic is then used here. Because int16 is then being used here the additions are also then done using int16, so it should then work.
ashrafkhatri



Joined: 06 May 2008
Posts: 14

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PostPosted: Mon Feb 27, 2017 3:15 am     Reply with quote

Thanks;
Code is now working
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