Programming Languages Course)

((Explain this code in details with drawing the stack))

Lab Exercise

Postfix Expression

#include

using namespace std;

int max_length = 10 ;

class postfix

{

private :

int stack[10] ;

int top,y, x ;

char *t ;

public :

postfix( ) ;

void setexpr ( char *str ) ;

void push ( int item ) ;

int pop( ) ;

void calculate( ) ;

void show( ) ;

} ;

postfix :: postfix( )

{

top = -1 ;

}

void postfix :: setexpr ( char *str )

{

t = str ;

}

void postfix :: push ( int item )

{

if ( top == max_length - 1 )

cout << endl << "Stack is full" ;

else

{

top++ ;

stack[top] = item ;

}

}

int postfix :: pop( )

{

if ( top == -1 )

{

cout << endl << "Stack is empty" ;

return NULL ;

}

int data = stack[top] ;

top-- ;

return data ;

}

void postfix :: calculate( )

{

int a, b, z ;

while ( *t )

{

if ( *t == ' ' || *t == ' ')

{

t++ ;

continue ;

}

if ( isdigit ( *t ) )

{

x = *t - '0' ;

push ( x ) ;

}

else

{

a = pop( ) ;

b = pop( ) ;

switch ( *t )

{

case '+' :

z =b + a ;

break ;

case '-' :

z = b- a ;

break ;

case '/' :

z = b / a ;

break ;

case '*' :

z = b * a ;

break ;

default :

cout << "This operator is unknown " ;

exit ( 1 ) ;

}

push ( z ) ;

}

t++ ;

}

}

void postfix :: show( )

{

y= pop ( ) ;

cout << "the result after the calculation is: " << y <

}

int main( )

{

char expr[10];

cout << " Enter the postfix expression that you want: " ;

cin.getline ( expr, max_length ) ;

postfix x ;

x.setexpr ( expr ) ;

x.calculate( ) ;

x.show( ) ;

system(pause)

return 0;

}