imread is not accepting my file name string

I have attached my test script and sample image. I'm trying to create a Matlab script to build image file names and open image files with imread. Here is my simple code that I CAN'T get to work. I don't see what I am doing wrong. I get an error saying Matlab imread needs an input file string - but I AM giving it a file string. What am I doing wrong?

If I type in the file name directly it works, like this:

inputImage = imread(RGB0.png);

But my script below does not work, why?

%----------  begin script here

clear;

f= 0 ;

inFileStr = 'xxxxxxxxxxxx';
finishedFileStr = 'yyyyyyyyyyyy';

% these test fprints indicate that I can create a valid file name.
inFileStr = "RGB%d.png";
finishedFileStr = sprintf(inFileStr, f);
fprintf('finished string = ');
fprintf(finishedFileStr);    
fprintf('\n');

% So why does the next line NOT work, I get the error:
%  "The file name or URL argument must be a character vector."

     inputImage=imread(finishedFileStr);  

% ---------- end script here

Answer 1

[Walter Roberson]

Change

inFileStr = "RGB%d.png";

to

inFileStr = 'RGB%d.png';