How to write the array into the sqlite database for Objective-C?

Inserting into the database is pretty much the reverse of reading from it. You don't say what the structure of your array is but here is some skeleton code you should be able to adapt to your needs:

// Assuming you have the sqlite database opened already
// sqlite3 *sqldb = ...;

// Also assuming you have an array of MyItems holding your data
// NSMutableArray *items = ...;

sqlite3_stmt *insert_statement;

// Prepare the insert statement
const char*sql = "INSERT INTO mytable (field1, field2, field3) VALUES(?,?,?)";
sqlite3_prepare_v2(sqldb, sql, -1, &insert_statement, NULL);

// Iterate over an array of dictionaries
for (MyItem *item in items) {

    // Bind variables - assumed to all be integers
    sqlite3_bind_int(insert_statement, 1, item.field1);
    sqlite3_bind_int(insert_statement, 2, item.field2);
    sqlite3_bind_int(insert_statement, 3, item.field3);

    // Execute the insert
    if (sqlite3_step(insert_statement) != SQLITE_DONE) {
        NSLog(@"Insert failed: %s", sqlite3_errmsg(sqldb));
    }

    // Reset the statement
    sqlite3_reset(insert_statement);
}

// release the statement
sqlite3_finalize(insert_statement);