I am not a programmer!

I can't code effectively at all. They say programming is just like learning a new language and I was terrible at that as well. The way I think my brain works is if I can just touch it. Even in my mind's eye if I can physically manipulate the problem then I can figure it out. Code and math, they're intangible and for decades I've tried to learn and for decades I've been just a beginner. (Note: if i write a question mark in parenthesis (?) it's just my way of using a term that I don't fully understand the meaning of)

Problem

I need to draw numbers on the screen (speed, RPM, temperature, etc) but the function that does this only accepts const char variables and my data contains integers. How do I convert the integers into a string so the function can work?

The SmartMatrix3 Arduino library has a function to draw text on the screen on an "indexed layer". Not sure exactly what the "indexed" means yet but looking at the Layer_Indexed.h file in libraries I see the following:

void drawChar(int16_t x, int16_t y, uint8_t index, char character);
void drawString(int16_t x, int16_t y, uint8_t index, const char text []);

We have the drawChar and drawString functions. drawChar displays a single ASCII character and drawString a text string (which as I understand it is just an array of char). The const part makes the string read-only, and the brackets at the end denotes an array.

Solutions

I've tried a few times to simply convert a two-digit integer into a string, and then pass that string as a variable to the drawString function. I get an error message every time.

invalid conversion from 'char' to 'const char*' [-fpermissive]

Notice the asterisk at the end of that error? I think it has something to do with a pointer(?) and I know pointers are versatile but I still don't understand it yet.

What's Next?

Well, you know how you can bit-bang data on a microcontroller? That's pretty much how my programming works. I'll brute force a solution until I get something that works. It would probably be easier to just post it on a forum somewhere, but the answers I get from those smarter than I only serve to daze and confuse. Well, let's get on with it....

Current test code (04/29/2016 10:09:08)

#include <SmartMatrix3.h>

#define COLOR_DEPTH 24                  // known working: 24, 48 - If the sketch uses type `rgb24` directly, COLOR_DEPTH must be 24
const uint8_t kMatrixWidth = 32;        // known working: 32, 64, 96, 128
const uint8_t kMatrixHeight = 32;       // known working: 16, 32, 48, 64
const uint8_t kRefreshDepth = 36;       // known working: 24, 36, 48
const uint8_t kDmaBufferRows = 4;       // known working: 2-4, use 2 to save memory, more to keep from dropping frames and automatically lowering refresh rate
const uint8_t kPanelType = SMARTMATRIX_HUB75_32ROW_MOD16SCAN;   // use SMARTMATRIX_HUB75_16ROW_MOD8SCAN for common 16x32 panels
const uint8_t kMatrixOptions = (SMARTMATRIX_OPTIONS_NONE);      // see http://docs.pixelmatix.com/SmartMatrix for options
const uint8_t kIndexedLayerOptions = (SM_INDEXED_OPTIONS_NONE);

SMARTMATRIX_ALLOCATE_BUFFERS(matrix, kMatrixWidth, kMatrixHeight, kRefreshDepth, kDmaBufferRows, kPanelType, kMatrixOptions);
SMARTMATRIX_ALLOCATE_INDEXED_LAYER(indexedLayer, kMatrixWidth, kMatrixHeight, COLOR_DEPTH, kIndexedLayerOptions);

const int defaultBrightness = 100 * (255 / 100);    // full brightness
                          //const int defaultBrightness = 15*(255/100);    // dim: 15% brightness

const char speedValue = 20;

void setup() {
  matrix.addLayer(&indexedLayer);
  matrix.begin();
  delay(3000);
}

void loop() {

  indexedLayer.fillScreen(0);

  indexedLayer.setFont(font8x13);
  indexedLayer.setIndexedColor(1, { 255, 255, 255 });
  indexedLayer.fillScreen(0);
  indexedLayer.drawString(24, 8, 1,speedValue);
  
  indexedLayer.swapBuffers(false);

 }