Snacking and dieting don't seem to go together. However snacks can be easily incorporated into a diet or healthy eating plan. Treats will prevent you from binging and over-eating feeling that you are missing out on certain foods. There are also a good choice of healthy snacks that can be enjoyed as an alternative.
If you cannot live without your favourite chocolate fix snack on a diet then make sure you incorporate the calories in your calorie intake. Remember as long as you burn more energy than you consume (and you have the right amount of vitamins and minerals and nutritional balance) you will be fine and will lose weight.
Ideally it would be good to substitute some processed, high-fat snacks with more natural or healthy snacks. Your taste buds can be trained to appreciate the sugars more in fruits and find sweet foods to sweet. In place of a chocolate bar (200-250 calories on average) try a wholemeal muffin with honey - less calories and fat and nutritionally better for you.