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Posted: **15 Jun 2011, 00:54**

Often I use text and number display functions to debug programs. I also use them a lot for NXT -> human interface in stable programs. I have recently been doing more with floating point numbers, and have seen several things I don't care for.

Here is a scenario:
I have a thermometer that is precise to about 0.02 degrees. I want to display the number in floating point, but I don't want it to read "24.1284", I want it to drop x number of exponents, so it will display "24.1". What I have been doing is calculating the temperature in floating point, multiplying by 10, setting it to a int, then setting it back to a float, and dividing it by 10. Sure, this makes it display "24.1", but when it is 24.0, it displays "24", which isn't what I want. That ".0" is very significant, and I want it displayed.

What I need to do is convert the number into a string and then display it as text. NumToStr works fine, but it drops exponent 0's, or anything in or beyond the 10,000th's place.

How do I do this? I came up with a clumsy function that does basically what I want, but I want to know how to do it "properly".

Posted: **15 Jun 2011, 02:53**

You use printf() in C. Not sure how much support NXC has for this, though:

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float x = 24.1284;
printf("%.1f", x);

If you want to store it in a string, use sprintf():

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float x = 24.1284;
string s = "";
sprintf(s, "%.1f", x);
TextOut(0, 0, s, 0);

Again, not sure if this actually works in NXC.

I really should figure this out for C++. All I can remember is that there's stringstream, and a whole bunch of other "flags"...

Posted: **15 Jun 2011, 03:06**

I'd indeed suggest printf() just as muntoo did. But there's also FormatNum(). You can look up the format strings in any C documentation, but you'll have to try out what NXC supports (I just have a nice link handy which happens to be for MATLAB, but the format specifiers should be the same). Maybe the %g is interesting for you, it should output significant digits of a float.

muntoo wrote: I really should figure this out for C++. All I can remember is that there's stringstream, and a whole bunch of other "flags"...

Yep, there are various stringstream examples. But I honestly got very annoyed with it. I then came accross

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std::cout.precision(n);

but that's not great either.
I currently use Qt's QString class, with the .arg() function, and I love it every day

. Especially as it takes care of Unicode once and for all (let's hope) and has also methods like .toStdStr() to convert to other formats...

Posted: **15 Jun 2011, 05:09**

Thanks both of you

I am now able to do what I want.

Posted: **15 Jun 2011, 06:43**

I normally use this:

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#define printf1( _x, _y, _format1, _value1) { \
  string sval1 = FormatNum(_format1, _value1); \
  TextOut(_x, _y, sval1); \
}

this wrap around FormatNum is exactly the same as what NXC does with it's printf macro.

you may use numbers (integer, fp) formatted like in ANSI C, but as a substitute to "\n" you may print at (x,y) like with NumOut or TextOut:

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printf1(0,40, "%5.2f", fpvar);      // OR: printf1(0,40, "var=%5.2f", fpvar);
printf1(0,32, "%10d", longvar);     // OR: printf1(0,32, "var=%10d", longvar);
printf1(0,24, "%06x", intVarAsHex); // OR: printf1(0,24, "var=%06x", intVarAsHex);

advantage: you need not to clear the line to avoid "overwriting" garbage printing shorter numbers after longer ones.

for strings you may write

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printf1(0, 8, "%s", stringvar);

- although it is sometimes not correctly interpreted by the firmware;
but if it should be faulty sometimes for strings you can use a workaround: pass your string by the Formatstring

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printf1(0,0, "write your string constant or variable", 0);

http://www.cplusplus.com/reference/clib ... io/printf/
http://en.wikipedia.org/wiki/Printf

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#define printf1( _x, _y, _format1, _value1) {     \
  string sval1=FormatNum(_format1, _value1);      \
  TextOut(_x, _y, sval1);                         \
}

task main(){

  int  i=1000;
  long l=87654321;
  float f= 123.45678;
  string msg="HUG ME!";

  printf1(0,56,"%6d",  i);  // 6 digits, rest space (%i = %d)
  printf1(0,48,"0x%04x",i); // 4 digits hex notation, rest Zeros + "0x" prefix 
  printf1(0,40,"%10d", l);  // 10 digits, rest space
  printf1(0,32,"%7.2f",f);  // 7 digits including 2 decimals, rest space
  printf1(0,16,"%s", msg);  // string output
  
  while(1);
}

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