Question: What I have:

```
char cmd[50] = "some text here";
char v[] = {'a','s','d','c','b'};

```

So I want to concatenate `cmd` by adding a letter from `v`.

Obviously: 

```
strcat(cmd, v[3]);

```

doesn't work because `strcat` doesn't accept the `v[n]` parameter `n = int`.

Answer: 
Hmm. As far as I understand you want to add a single char from the second array?
so you have to use

```
  strncat (cmd, &v[3], 1);

```

:-)
```
char buf[2];

sprintf(buf,"%c", V[3]);
strcat(cmd, buf);

```

or 

```
strncat (cmd, &v[3],1);

```

you can not do it with

```
strcat(cmd,&v[3]);

```

this will coppy the V array from cell 3 to the end of array and not copy only V[3]

I can suggest another solution

```
int len = strlen(cmd);
cmd[len]=v[3];
cmd[len+1] = '\0';

```