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rblue
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| negative floating values |
 Posted: Wed Apr 04, 2007 12:20 pm |
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hi every one
i have a problem in displaying negative float values...
i am using a Graphic LCD with 160x128 pixels and t6963 controller.
i am displaying a graph with it is a cursor which displays both the values of x and y axis
y axis is no problem as it is a long int and all positive values
x- axis has to be scalled and the resultant values are float
so here is my code...
| Code: |
if( !SW3 )
{
x=x-1;// to move cursor left
remove_cursor(x+1,y);// remove old cousor .. i have a routine
cursor(x,y);// place cursor in new position
sprintf( array, "%3.2f",(x-19)/4.0 );//the x-axis value is scalled and string made
glcd_text35( 110,9 , array, 1 );// display the vale at my described location
}
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now the problem is when value of x falls bellow 19 it should display a negative value instead it is displaying a positive value
that is
63.74 it should show -0.74
63.49 it should show -0.49
63.24 it should show -0.24
any suggestions or help from an expert i want to display negative values |
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Ttelmah
Guest
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| Posted: Wed Apr 04, 2007 12:44 pm |
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'x' is presumably declared as an integer. Hence it is by default 'unsigned'. The arithmetic (x-19), is performed in integer (since both values are integers). Hence it wraps, giving a positive number 256 greater than the right value. You can correct this a whole number of ways:
(x-19.0) will force this arithmetic to use a 'float' type.
((signed)x-19) will convert x to a signed type, and use signed arithmetic.
((float)x-19) will convert x to a float then perform the arithmetic.
Best Wishes |
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