One easy way to control how data is written to the file is to use fprintf. This is identical to the printf except that the first parameter is where the information will be written to.
Example:
FILE *ficheiro = fopen ("teste.txt","w");
struct televisao tv;
//preencher tv com os dados que interessam
fprintf (ficheiro,"%d,%d,%d,%d,%s\n",tv.id_guit, tv.precodia, tv.preco, tv.estado,tv.nome);
fclose (ficheiro);
In this example I used , as a separator, which acts as if creating a file csv, however, the format in which the data is written to the file is entirely at your discretion.