1. Stacks CISC181 Spring 2004 P. T. Conrad University of Delaware

2. stacks: push and pop

3. stack: last in, first out (lifo) 3 only the thing on top of the stack is accessible push: add something on top of the stack pop: remove something from the top of the stack (and return it as the result of the pop operation) initial stack after: push(3) 11 3 after: push(11) -2 11 3 after: push(-2) 11 3 after: pop (returns -2) 7 11 3 after: push(7) 11 3 after: pop (returns 7)

4. "a stack" vs. "the stack" computer systems use lots of stacks –laser printers use stacks to process PostScript –compilers use stacks to convert C++ into a.out –stacks are used to process HTML code "a stack" means "any old stack" but when we say "the stack", we mean a specific one: the "run-time stack" –we use it to keep track of function calls –we use it to store local automatic variables (most variables we've seen so far are local automatic variables)

5. run-time stack call a function: push return from a function: pop main sumSquares squared i n answer i y

6. run-time stack for factorial call a function: push return from a function: pop main fact i=4 x=4 fact i=3 fact i=2 fact i=1... int factorial(int i) { if (i<=1) return 1; else return i * factorial (i – 1); } int main(void) { int x=4; cout << factorial(x); return 0; } return 1 return 2 * 1 = 2 return 3 * 2 = 6 return 4 * 6 = 24 cout << 24;