## The problem

```
i=01;
j=01;
['F',num2str(i), '_', num2str(j),'.mat']
```

evaluates to

F1_1.mat

and not to

F01_01.mat

as expected.

The reason for this is that `i=01`

is a double type assignment and `i`

equals to `1`

– there are no leading zeros for these types of variables.

## A solution

a possible solution for the problem would be

```
for ii = 1:11
for jj= 1:11
filename = sprintf('F_%02d_%02d.mat', ii, jj );
load(filename);
Func(Fi_j); % run the function for each file Fi_j
end
end
```

### Several comments:

Note the use of

`sprintf`

to format the double`ii`

and`jj`

with leading zero using`%02d`

.You can use the second argument of

`num2str`

to format its output, e.g.:`num2str(ii,'%02d')`

.It is a good practice to use string formatting tools when dealing with strings.

It is a better practice in matlab

**not**to use`i`

and`j`

as loop counters, since their default value in matlab is`sqrt(-1)`

.