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Unsaturated hydrocarbons are organic compounds containing at least one double bond (alkenes, e.g., C=C) or triple bond (alkynes, e.g., C≡C). These compounds can have more than one double or triple bond in their structure.

The parent chain is the longest continuous chain of carbon atoms in the molecule. This chain may or may not include the double or triple bond. It is essential to choose the longest chain of carbons first, and then look for additional functional groups or bonds within the chain.

Once the parent chain is selected, locate and count the number of double and triple bonds within the parent chain. If there are no double or single bonds in the parent chain, then the hydrocarbon is saturated (meaning it is an alkane).

Number the carbons in the parent chain, starting from the end that is closest to the first double or triple bond. Assign a number (locant) to each carbon atom that is part of any double or triple bond. If there's any additional double or triple bonds, assign the locants of those subsequent bonds as well.

Name the compound using IUPAC rules. The parent chain's name is based on the number of carbons and the suffixes '-ene' for alkenes (indicating the presence of double bonds) and '-yne' for alkynes (indicating the presence of triple bonds). Put the locant(s) before the suffix, separated by a hyphen, to indicate the position of the double or triple bond in the parent chain. If there are multiple double or triple bonds, list the locants separated by commas. For example, for the hydrocarbon CH3-CH=CH-CH3, the name would be but-2-ene, where but- signifies that the parent chain has four carbons, -2- indicates the double bond's location between the second and third carbons, and the suffix -ene indicates that it is an alkene (with double bond). In summary, the position of a double or triple bond in the longest continuous chain of an unsaturated hydrocarbon is indicated by assigning locants to the carbon atoms involved in the bond and including the locant(s) in the compound's IUPAC name.