InFix PreFix PostFix Notation A Level Computer Science

In-Fix Pre-Fix Post-Fix Notation A Level Computer Science

Methods of Notation • 4+2 • In-fix • +42 • Pre-fix • Polish Notatation • 42+ • Post-fix • Reverse Polish Notation (RPN)

Infix to RPN Examples • • • 2*(A+B) (Infix) 2*(AB+) x*y xy* 2 AB+* (RPN)

Infix to RPN Examples • • • (A+B)*2 (Infix) (AB+)*2 x*y xy* AB+2* (RPN)

Infix to RPN Examples • • • (A+B)/(C*D) (Infix) (AB+)/(CD*) x/y xy/ AB+CD*/ (RPN)

Infix to RPN Examples • • ((1 + 2) * 4) + 3 (Infix) ((12+)*4)+3 (x*y)+z (xy*)+z (12+4*)+3 x+y xy+ 12+4*3+ (RPN)

Binary Tree – Post Order + * a • Post Order • ab*c+ c b

Infix to Post Fix Conversion using Stacks Order of precedence for operators * / + If an operator is pushed onto stack and the operator below it is of higher or equal precedence remove bottom item from stack • If an operator is pushed onto stack and the operator below it is of a lower precedence operators remain on stack • •

Infix to Post Fix Conversion using Stacks • • 4 + 2 * 5 (Infix) 4 2 5 * + (RPN) * + Stack 42 5 * + String

Infix to Post Fix Conversion using Stacks • 4 * 2 + 5 (Infix) • 4 2 * 5+ (RPN) + * + Stack 42*5 + String

Infix to Post Fix Conversion using Stacks • 4 - 2 + 5 (Infix) • 4 2 – 5 + (RPN) + + Stack 42 - 5 + String

Infix to Post Fix Conversion using Stacks • 4 / 2 * 5 (Infix) • 4 2 / 5 * (RPN) * / * Stack 42/ 5 * String

Evaluate RPN in Stack • ab*c+ • (a*b)+c (Infix) • • Push operands When reach operator evaluate previous 2 operands Pop 2 operands Push evaluation a b a (a*b) c (a*b)+c

Evaluate RPN in Stack • • • fgh*+ f+(g*h) (Infix) f=3 g=4 h=5 3 4 3 5 4 3 (4*5)20 3 3+(4*5)23 3