CITS2002 Systems Programming  
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Adding items to our stack data structure

As a program's execution progresses, we'll need to add and remove data items from the data structure.

The need to do this is not known until run-time, and data (perhaps read from file) will determine how large our stack eventually grows.

As its name suggests, when we add items to our stack, we'll speak of pushing new items on the stack, and popping existing items from the stack, when removing them. 


typedef struct _s {     // same definition as before   
    int         value;
    struct _s   *next;
}  STACKITEM;

STACKITEM    *stack = NULL;

 ....

void push_item(int newvalue)
{
    STACKITEM  *new = malloc( sizeof(STACKITEM) );  

    if(new == NULL) {     // check for insufficient memory   
        perror( __func__ );
        exit(EXIT_FAILURE);
    }

    new->value   = newvalue;
    new->next    = stack;
    stack        = new;
}

The functions push_item and pop_item are quite simple, but in each case we must worry about the case when the stack is empty.
We use a NULL pointer to represent the condition of the stack being empty.

 

CITS2002 Systems Programming, Lecture 19, p3, 3rd October 2023.