How to concat string + i?

according to this it looks like you have to set "N" before trying to use it and it looks like it needs to be an int not string? Don't know much bout MatLab but just what i gathered from that site..hope it helps :)

You can concatenate strings using strcat. If you plan on concatenating numbers as strings, you must first use num2str to convert the numbers to strings.

Also, strings can't be stored in a vector or matrix, so f must be defined as a cell array, and must be indexed using { and } (instead of normal round brackets).

f = cell(N, 1);
for i=1:N
f{i} = strcat('f', num2str(i));
end

For versions prior to R2014a...

One easy non-loop approach would be to use genvarname to create a cell array of strings:

>> N = 5;
>> f = genvarname(repmat({'f'}, 1, N), 'f')


f =


'f1'    'f2'    'f3'    'f4'    'f5'

For newer versions...

The function genvarname has been deprecated, so matlab.lang.makeUniqueStrings can be used instead in the following way to get the same output:

>> N = 5;
>> f = strrep(matlab.lang.makeUniqueStrings(repmat({'f'}, 1, N), 'f'), '_', '')


f =
1×5 cell array


'f1'    'f2'    'f3'    'f4'    'f5'

Let me add another solution:

>> N = 5;
>> f = cellstr(num2str((1:N)', 'f%d'))
f =
'f1'
'f2'
'f3'
'f4'
'f5'

If N is more than two digits long (>= 10), you will start getting extra spaces. Add a call to strtrim(f) to get rid of them.

As a bonus, there is an undocumented built-in function sprintfc which nicely returns a cell arrays of strings:

>> N = 10;
>> f = sprintfc('f%d', 1:N)
f =
'f1'    'f2'    'f3'    'f4'    'f5'    'f6'    'f7'    'f8'    'f9'    'f10'

Try the following:

for i = 1:4
result = strcat('f',int2str(i));
end

If you use this for naming several files that your code generates, you are able to concatenate more parts to the name. For example, with the extension at the end and address at the beginning:

filename = strcat('c:\...\name',int2str(i),'.png');

Using sprintf was already proposed by ldueck in a comment, but I think this is worth being an answer:

f(i) = sprintf('f%d', i);

This is in my opinion the most readable solution and also gives some nice flexibility (i.e. when you want to round a float value, use something like %.2f).