Help in C++ please!

Read a postfix expression from an input file. Evaluate the postfix format and display the results Precondition: The expression will be read from a file (input.txt) that contains a single line. There will be no spaces between the operands and the operators. The following operators are allowed: +-* / o The normal rules of precedence will apply. No error checking is necessary. The numbers will all be greater than 0 and less than 10 (positive, single digit numbers) Example: 12+ Result is