generate a name in c randomly

 signed char *tab_alphabet[]={"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z","\0"};

int nombreAlea(int min, int max){
      return (rand()%(max-min+1) + min);
    }
void generer_name(int length,signed char* n){
  int i ;
  signed char *j;
  for (i=0;i<length;i++){
    int k = nombreAlea(1,26);// from the table of the alphabet
    j = tab_alphabet[k-1];
    strcat(n,j); 
  }
}

here s the main :

int main () {
    int a = nombreAlea(4,30);
   signed char *nn;
    generer_name(a,nn);
    return 0 ;
}

The problem is that the result always is preceeded with "a!!@" , any help , i have a doubt on the strcat