Stack algorithm

[Dwight Sturrock]

Here are a few stack functions I wrote as part of a larger C++ program. The function names and comments are fairly self explanatory. My approach was fairly straightforward. I discovered there are many special cases that have to be accounted for when emulating RPN stack dynamics.

PHP Code:

void enter_pressed(bool *enter_was_pressed_)
    {
    t=z;
    z=y;
    y=x;
    //x=x
    write_stack();
    *enter_was_pressed_=1;
    //after an enter I should be able to overwrite x
    } 


PHP Code:

void add_pressed(bool *a_function_was_executed_, bool *decimal_fraction_)
    {
    //z=z
    x=y+x;    //perform math first
    y=z;
    z=t;
    *a_function_was_executed_=1;    //after a function is executed, stack lift must be enabled
    *decimal_fraction_=0;            //since a function has been executed, we are back on the left side of the decimal point
    write_stack();
    } 


PHP Code:

void space_pressed (bool *decimal_fraction_, bool *a_function_was_executed_, bool *enter_was_pressed_, bool *decimal_point_just_pressed_)    
    //space is the CLEAR STACK key
    {
        t=0;
        z=0;
        y=0;
        x=0;
        w=0;
        place_value=10;
        *decimal_fraction_=0;            //clear all flags:
        *a_function_was_executed_=0; 
        *enter_was_pressed_=0;
        *decimal_point_just_pressed_=0;
        write_stack();
    } 


PHP Code:

void tab_pressed()    //tab is the CHS key
    {
    x=x*(-1);
    write_stack();
    } 


PHP Code:

void roll_up_pressed(bool *a_function_was_executed_)
    {
    w=t;
    t=z;
    z=y;
    y=x;
    x=w;
    *a_function_was_executed_=1;    //rolling the stack requires the a_function_was_executed flag to be set for proper stack lift
    write_stack();
    }