user20713: My C is rusty, so please forgive this simple problem.
This line works:
Tft.drawString("Test",200,200,2,WHITE);
But, this has compile errors:
String yStr = "Test";  
Tft.drawString(yStr,200,200,2,WHITE);  

The function in the library:
void drawString(char *string,unsigned int poX, unsigned int poY,unsigned int size,unsigned int fgcolor);

The error is "no known conversion for argument 1 from 'String' to 'char*'".
Conclusion - I need a character array. Here's what I am trying to accomplish.
I have two integers that I would like to display on my Tft screen. For example, 225 and 250 to be displayed as "225,250".
I haven't figured out a way to build the char array for the drawString() function.
Assistance would be appreciated.

Thanks for the quick reply Ignacio.
I tried that, but the compiler still doesn't like it.
Here's how I built the string:
string stringXY ;
stringXY += xStr;
stringXY += ",";
stringXY += yStr;
Tft.drawString(stringXY.c_str(),200,200,2,RED);  

Error: invalid conversion from 'const char*' to 'char*' [-fpermissive]
I am apparently using c_str() wrong?

user368: Put it in a String and then use the c_str() method to get the associated char*.

user20713: Many thanks to Ignacio.
I changed the function in the library to:
void drawString(const char *string,unsigned int poX, unsigned int poY,unsigned int size,unsigned int fgcolor);
This fixed the problem and gave me more confidence in my vague understanding of C.

user84: Another option in your situation is to not use String at all (which is preferrable for reasons I won't explain here) and exclusively use plain old C strings and their associated functions:
// Define a string buffer to hold the result, ensure it is long enough
// to hold "N1,N2". An additional char must be added to terminate the string with 0
char result[15+1];
unsigned int N1 = ...;
unsigned int N2 = ...;
// Format output as desired
sprintf(result, "%u,%u", N1, N2);
// Now you can use result with drawString
Tft.drawString(result, 200, 200, 2, RED);

sprintf is a very powerful formatting function that offers you plenty of options.
Note that I took it for granted that your numbers are unsigned int; if these were normal integer (possibly negative), you should replace "%u,%u" with "%d,%d".

20713: <p>My C is rusty, so please forgive this simple problem.</p>

<p>This line works:</p>

<p><code>Tft.drawString("Test",200,200,2,WHITE);</code></p>

<p>But, this has compile errors:</p>

<pre><code>String yStr = "Test";  
Tft.drawString(yStr,200,200,2,WHITE);  
</code></pre>

<p>The function in the library:</p>

<pre><code>void drawString(char *string,unsigned int poX, unsigned int poY,unsigned int size,unsigned int fgcolor);
</code></pre>

<p>The error is <strong>"no known conversion for argument 1 from 'String' to 'char*'"</strong>.</p>

<p>Conclusion - I need a character array. Here's what I am trying to accomplish.</p>

<p>I have two integers that I would like to display on my Tft screen. For example, 225 and 250 to be displayed as "225,250".</p>

<p>I haven't figured out a way to build the char array for the <code>drawString()</code> function.</p>

<p>Assistance would be appreciated.</p>

<hr>

<p>Thanks for the quick reply Ignacio.<br>
I tried that, but the compiler still doesn't like it.</p>

<p>Here's how I built the string:</p>

<pre><code>string stringXY ;
stringXY += xStr;
stringXY += ",";
stringXY += yStr;
Tft.drawString(stringXY.c_str(),200,200,2,RED);  
</code></pre>

<p>Error: <strong>invalid conversion from 'const char*' to 'char*' [-fpermissive]</strong></p>

<p>I am apparently using <code>c_str()</code> wrong?</p>
 368: <p>Put it in a <a href="https://www.arduino.cc/en/Reference/StringObject" rel="nofollow"><code>String</code></a> and then use the <code>c_str()</code> method to get the associated <code>char*</code>.</p>
 20713: <p>Many thanks to Ignacio.</p>

<p>I changed the function in the library to:</p>

<p>void drawString(<strong>const</strong> char *string,unsigned int poX, unsigned int poY,unsigned int size,unsigned int fgcolor);</p>

<p>This fixed the problem and gave me more confidence in my vague understanding of C.</p>
 84: <p>Another option in your situation is to not use <code>String</code> at all (which is preferrable for reasons I won't explain here) and exclusively use plain old C strings and their associated functions:</p>

<pre><code>// Define a string buffer to hold the result, ensure it is long enough
// to hold "N1,N2". An additional char must be added to terminate the string with 0
char result[15+1];
unsigned int N1 = ...;
unsigned int N2 = ...;
// Format output as desired
sprintf(result, "%u,%u", N1, N2);
// Now you can use result with drawString
Tft.drawString(result, 200, 200, 2, RED);
</code></pre>

<p><code>sprintf</code> is a very powerful formatting function that offers you plenty of options.</p>

<p>Note that I took it for granted that your numbers are <code>unsigned int</code>; if these were normal <code>integer</code> (possibly negative), you should replace <code>"%u,%u"</code> with <code>"%d,%d"</code>.</p>
