Looks like you have it essentially right; you just need to use the decimal specifier %d (or %03d or whatever makes sense) rather than the string specifier %s in the sprintf format for the index p (and maybe some underscores for readability):
% Made up variables.
dataDirectory = '';
fileNameRoot = 'result';
modulationTypes = ["QAM" "PSK"];
modType = 1;
numFramesPerModType = 2;
for SNR=[-20,-10,0,10,20,30]
for p=1:numFramesPerModType
fileName = fullfile(dataDirectory,...
sprintf("%s_%s_%d_%03d_SNR",fileNameRoot,modulationTypes(modType),p,SNR))
end
end
The way you had it, with %s for p, the file names each contain a non-alphanumeric character (characters whose ASCII code is 1, 2, etc.). These gave me an error when using save() on my version of MATLAB, but here they seemed ok. In any case, if you want to see the value of p in the file name, use some variant of %d instead of %s.
