Conversion from infix to prefix using stack
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This document is a data structures assignment that contains two tasks: 1) Converting an infix expression to postfix notation using a stack. The example infix expression is converted to postfix as -+-AB*C+DE+FG. 2) Evaluating the postfix expression from the first task by assigning values to variables and using a stack to calculate the result, which is 33.
Conversion from infix to prefix using stack
- 1. DATA STRUCTURE ASSIGNMENT #2 Comsats institute Of Information Technology Islamabad Subject : Data Structure Assignment#: 2 Submitted to: Sir Zaheer Ul Hassan Sani Submitted by: Haq Nawaz Reg#: Sp12-bcs-089 Submission date: 2 November 2013 SP12-BCS-089 Page 1
- 2. DATA STRUCTURE ASSIGNMENT #2 Task a: We have infix expression in the form of: ((A-B)+C*(D+E))-(F+G) Now reading expression from right to left and pushing operators into stack and variables to output stack Input ) G + F ( ) ) E + D ( * C + ) B A ( ( EMPTY SP12-BCS-089 Output_stack EMPTY G G GF GF+ GF+ GF+ GF+ GF+E GF+E GF+ED GF+ED+ GF+ED+ GF+ED+C GF+ED+C* GF+ED+C* GF+ED+C*B GF+ED+C*B GF+ED+C*BA GF+ED+C*BAGF+ED+C*BA-+ GF+ED+C*BA-+- Stack ) ) )+ )+ EMPTY -) -)) -)) -))+ -))+ -) -)* -)* -)+ -)+) -)+) -)+)-)+)-)+ EMPTY Page 2
- 3. DATA STRUCTURE ASSIGNMENT #2 Out put_stack = GF+ED+C*BA-+Reversing the output_stack we get prefix expression: -+-AB*C+DE+FG Task b: Evaluating the prefix expression: Assigning the values to variables A=7 B=6 C=5 D=4 Reading expression from right to left: reading 1 2 + 3 4 + 5 * 6 7 + - operation 1 12 12+ 33 334 3 3 4+ 375 3 7 5* 3 35 6 3 35 6 7 3 35 6 73 35 1+ 3 36 - E=3 F=2 G=1 Stack_output Empty 3 3 3 37 37 3 7 35 3 35 3 35 3 35 1 3 36 33 Pop stack_output : 33 Result=33 SP12-BCS-089 Page 3
- 4. DATA STRUCTURE ASSIGNMENT #2 Comparing both expressions evaluations: ((A-B)+C*(D+E))-(F+G) ((7-6)+5(4+3))-(2+1) (1+5*7)-3 1+35-3 36-3 33 SP12-BCS-089 Page 4