Converting Infix to Postfix
Example: (A + B) * C
symb postfix stack
( (
A A (
+ A ( +
B AB ( +
) AB +
* AB + *
C AB + C *
AB + C *
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Converting Infix to Postfix and Implementing Stacks in C++, Slides of Data Structures and Algorithms
An example of converting an infix expression to postfix notation using a stack. It also explains how to implement a stack in c++ using templates. The code for a stack class and its implementation.
Typology: Slides
2011/2012
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Converting Infix to Postfix
Example: (A + B) * C
symb postfix stack
A A (
+ A ( +
B AB ( +
) AB +
* AB + *
C AB + C *
AB + C *
C++ Templates
We need a stack of operands and a stack
of operators.
Operands can be integers and floating
point numbers, even variables.
Operators are single characters.
We would have to create classes
FloatStack and CharStack.
Yet the internal workings of both classes is
the same.
Stack using templates
Stack.h:
template
class Stack {
public:
Stack(); int empty(void); // 1=true, 0=false int push(T &); // 1=successful,0=stack overflow T pop(void); T peek(void); ~Stack();
private:
int top; T* nodes;
};
Stack using templates
Stack.cpp
#include <iostream.h> #include <stdlib.h> #include "Stack.cpp"
#define MAXSTACKSIZE 50
template
Stack using templates
Stack.cpp
template
int Stack
{
if( top < MAXSTACKSIZE ) {
nodes[++top] = x; return 1;
}
cout << "stack overflow in push.\n";
return 0;
}
Stack using templates
Stack.cpp
template
Function Call Stack
Stacks play a key role in implementation of
function calls in programming languages.
In C++, for example, the “call stack” is
used to pass function arguments and
receive return values.
The call stack is also used for “local
variables”
Call Stack
In GCC, a popular C/C++ compiler on Intel
platform, stack entries are:
return address
first argument
second argument
last argument ……….
n*4(%esp)
(%esp) top
8(%esp)
4(%esp)
Call Stack
Example: consider the function:
int i_avg (int a, int b) { return (a + b) / 2; }
.globl _i_avg
_i_avg:
movl 4(%esp), %eax
addl 8(%esp), %eax # Add the args
sarl $1, %eax # Divide by 2
ret # Return value is in %eax