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printf statement

 
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hemnath



Joined: 03 Oct 2012
Posts: 242
Location: chennai

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printf statement
PostPosted: Thu Oct 05, 2017 12:59 am     Reply with quote
I want to print the data with different decimal point based on the condition.
Below is the sample code.
Code:

// different decimal point
const float pressure_display[3][8] = {   {5.1, 5.2, 5.0, 5.2, 5.2, 5.2, 5.3, 5.2},
                              {5.0, 5.1, 5.0, 5.1, 5.1, 5.1, 5.2, 5.1},
                              {5.0, 5.1, 5.0, 5.1, 5.1, 5.1, 5.2, 5.1}
                           };

float data;

// in main loop
 data = 12345678;

// how to write the print statement to display the data with different decimal point.
printf(lcd_data, "%", data); // how to call decimal point

Please help.
Ttelmah



Joined: 11 Mar 2010
Posts: 19552

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PostPosted: Thu Oct 05, 2017 1:47 am     Reply with quote
First thing, forget float!......

Float gives only about 6 digits of actual precision. If your number is something like 3.33 for example, it'll actually be stored as 3.32999. Not good.

Now, if your numbers were meant to be float format specifiers, they wouldn't work anyway. In C, the number in front of the decimal point is the _total field width_ (so how much space to allow for the whole output), which is then followed by the decimal and the digits to put after the decimal. So 5.1, is actually a number formatted as xxx.x five characters total.

Then format specifiers can't be variables handed to the function. You have to understand that all the layout maths is done by the compiler _before the code ever runs_. So the way to have variable decimals, would be:

Code:

void display_val(int32 number, int8 decimals)
{
    switch(decimals) {
    case 0:
       printf(lcd_data, "%9.0LW", number);
       break;
    case 1:
       printf(lcd_data, "%9.1LW", number);
       break; 
    case 2:
       printf(lcd_data, "%9.2LW", number);
       break; 
    case 3:
       printf(lcd_data, "%9.3LW", number);
       break;
    default: 
       printf(lcd_data, "%9.1LW", number);
       break;
    }
}

//then design your code to give an integer value not a float
//integer 'millivals', or 'centivals' for thousandths, hundredths etc..

   int32 data;
   
   data = 12345678;
   display_val(data,1); //will output 1234567.8
   display_val(data,2); //will output 123456.78
   //etc..
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