Hey Indhumathi! B.com is undergraduate degree in commerce where as chartered accountant CA is professional courses having 3 level you have  every level, it takes 4 years to give CA final examination if you clear your every exam in first attempt. 

I would suggest you to choose b. Com honours if you want to make career in CA as subjects  are almost same. But yes, CA demand high discipline and hard working because It's is a professional course and it demand high practice and knowledge of students to get perfection in each and every concepts and papers are also tough compare  to B.  Com

When you will prepare for CA, B. Com itself seems easy for you and it will be best courses doing along with CA. 

You will notice the similarity of subjects in different semesters of B. Com and  CA IPCC course and CA final Example : financial accounting, cost accounting, direct and indirect tax, corporate accounting, finanacial management, auditing these are courses you will study in different semesters of b. Com and in CA IPCC and some topic and  subjects  in CA final.

CA foundation is the entrance exam which is first level .All your 11th and 12th syllabus cover if your are from commerce stream in financial accounting and in maths for quantative aptitude. 

Hope this helps

God luck!