I have dry cough for 5 days. it is not very severe. will prospan cough syrup be useful?

Unlikely.: Prospan is a tincture of ivy in alcohol. The alcohol content is very high. There is scant evidence that ivy is an effective cough suppressant in well-controlled trials; the sedative effect of the alcohol is probably the mechanism by which this has any cough suppression activity at all. Consider dextromethorphan, honey, or medicines with benzonatate or a tiny amount of narcotic for relief.

Maybe : This is an OTC herbal medicine for cough in general, may be helpful in your case, read the labels carefully though. If it doesn't help you need to see your doctor, good luck

Do not smoke: In the absence of fever or other symptoms it usually makes no difference what you do after only 5 days. Albuteral inhaler may help. Elixer of guaifenesin and dextromethorphan is somewhat effective. Stay away from any smoke. Juice from ivy leaves is a placebo.