evaluating postfix expression requires the use of stack to store the operands or variables at the beginning of the expression until they are needed assume we are given valid postfix expression stored in string consisting of operators and single-letter variables we can evaluate the expression by scanning the stringone character or token at time for each tokenwe perform the following steps if the current item is an operandpush its value onto the stack if the current item is an operator(apop the top two operands off the stack (bperform the operation (note the top value is the right operand while the next to the top value is the left operand (cpush the result of this operation back onto the stack the final result of the expression will be the last value on the stack to illustrate the use of this algorithmlet' evaluate the postfix expression from our earlier example assume the existence of an empty stack and the following variable assignments have been madea the complete sequence of algorithm steps and the contents of the stack after each operation are illustrated in table token alg step abc+* abc+* abc+* abc+* ( pop top two valuesy ( compute or ( abc+*dstack description push value of push value of push value of push result ( of the addition (apop top two valuesy (bcompute or (cpush result ( of the multiplication abc+* abc+* (apop top two valuesy (bcompute or ( push value of push result ( of division table the stack contents and sequence of algorithm steps required to evaluate the valid postfix expression