Black stool. What should i do for that?

Sir, i was in problem of gas in stomach for two days,(there was pain in stomach also) so i have taken 2 tablet of meftal spas, but no benefit, So on third day i have taken Aciloc Rd (2 tablet within 5 hour , (in night)), and after that i feel relief, (i have also taken 1 tab of meftal spas and one packet of Eno) On next morning , i feel more better, but when i go for bathroom, i have noticed black stool but texture and smell was normal, (only color of stool was black and rest things was normal) , on same day in evening the color of stool was same (i have seen stool very closely, red blood sample was not seen). And i feel nothing abnormal, everything is same as usual. I m worried about black stool. Is it a serious problem? What should i do for that? (Diet was normal, no change in diet, but i have eaten some fast food in night, i.e. chowmin and egg roll, i am also addicted to smoking,) Pls rply me as soon as possible