Stacks

This is a discussion on Stacks within the C Programming forums, part of the General Programming Boards category; I need to write function retrieve to return the value at the top of the stack. The stack is not ...

  1. #1
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    Apr 2008
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    Stacks

    I need to write function retrieve to return the value at the top of the stack. The stack is not changed. Any suggestions.
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    typedef char stack_element_t;
    
    typedef struct stack_node_s
    {
    	stack_element_t element;
    	struct stack_node_s *restp;
    }stack_node_t;
    
    typedef struct 
    {
    	stack_node_t *topp;
    }stack_t;
    
    
    void push (stack_t *sp, stack_element_t c);
    stack_element_t pop(stack_t *sp);
    int retrieve (stack_t s);
    
    int main (void)
    {
    	stack_t s = {NULL};
    
    	push(&s, '2');
    	push(&s, '3');
    	push(&s, '4');
    
    	printf("\nEmptying stack: \n");
    	while (s.topp !=NULL)
    	{ 
    		printf("%c\n", pop(&s));
    		printf("%c\n", top);
    	}
    
    return (0);
    }
    
    void push(stack_t *sp, stack_element_t c)
    {
    	stack_node_t *newp;
    
    	newp = (stack_node_t *) malloc (sizeof (stack_node_t));
    	newp->element = c;
    	newp->restp = sp->topp;
    	sp->topp = newp;
    }
    
    
    stack_element_t pop(stack_t *sp)
    {
    	stack_node_t *to_freep;
    	stack_element_t ans;
    	
    	to_freep = sp->topp;
    	ans = to_freep->element;
    	sp->topp = to_freep->restp;
    	free(to_freep);
    
    	return (ans);
    }
    
    
    int retieve(stack_t s)
    {
    	stack_t element_t top;
    	return (top);
    }

  2. #2
    CSharpener vart's Avatar
    Join Date
    Oct 2006
    Location
    Rishon LeZion, Israel
    Posts
    6,484
    Code:
    int retieve(stack_t s)
    {
    	stack_t element_t top;
    	return (top);
    }
    if yuo have written pop I do not understand your prolems with retrieve... Are you sure it is your code?

    Code:
    stack_element_t retieve(stack_t s)
    {
    	stack_element_t top = s.topp->element;
    	return (top);
    }
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  3. #3
    Registered User
    Join Date
    Apr 2008
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    41
    the program works minus retrieve function. i cant figure out how to write the retrieve function to do wat i want it to do

  4. #4
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    Join Date
    Apr 2008
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    41
    Ok I figured that out. now i need to scan in a interger expression in postfix form and display its result. push each interger on the stsck. when an operand is encountered the top two operands are popped and the operation preformed. result is pushed back onto the stack. the final result should is the value remaning at the end when the expression is reached.

    I know how the postfix works but how do you write what to do when it encounters an operand?

    Any suggestions.

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