long pham - Page 50 - Developer IT

Why is my Pre to Postfix code not working?

- by Anthony Glyadchenko

For a class assignment, I have to use two stacks in C++ to make an equation to be converted to its left to right equivalent: 2+4*(3+4*8) -- 35*4+2 -- 142 Here is the main code: #include <iostream> #include <cstring> #include "ctStack.h" using namespace std; int main (int argc, char * const argv[]) { string expression = "2+4*2"; ctstack *output = new ctstack(expression.length()); ctstack *stack = new ctstack(expression.length()); bool previousIsANum = false; for(int i = 0; i < expression.length(); i++){ switch (expression[i]){ case '(': previousIsANum = false; stack->cmstackPush(expression[i]); break; case ')': previousIsANum = false; char x; while (x != '('){ stack->cmstackPop(x); output->cmstackPush(x); } break; case '0': case '1': case '2': case '3': case '4': case '5': case '6': case '7': case '8': case '9': cout << "A number" << endl; previousIsANum = true; output->cmstackPush(expression[i]); break; case '+': previousIsANum = false; cout << "+" << endl; break; case '-': previousIsANum = false; cout << "-" << endl; break; case '*': previousIsANum = false; cout << "*" << endl; break; case '/': previousIsANum = false; cout << "/" << endl; break; default: break; } } char i = ' '; while (stack->ltopOfStack > 0){ stack->cmstackPop(i); output->cmstackPush(i); cout << i << endl; } return 0; } Here is the stack code (watch out!): #include <cstdio> #include <assert.h> #include <new.h> #include <stdlib.h> #include <iostream> class ctstack { private: long* lpstack ; // the stack itself long ltrue ; // constructor sets to 1 long lfalse ; // constructor sets to 0 // offset to top of the stack long lmaxEleInStack ; // maximum possible elements of stack public: long ltopOfStack ; ctstack ( long lnbrOfEleToAllocInStack ) { // Constructor lfalse = 0 ; // set to zero ltrue = 1 ; // set to one assert ( lnbrOfEleToAllocInStack > 0 ) ; // assure positive argument ltopOfStack = -1 ; // ltopOfStack is really an index lmaxEleInStack = lnbrOfEleToAllocInStack ; // set lmaxEleInStack to max ele lpstack = new long [ lmaxEleInStack ] ; // allocate stack assert ( lpstack ) ; // assure new succeeded } ~ctstack ( ) { // Destructor delete [ ] lpstack ; // Delete the stack itself } ctstack& operator= ( const ctstack& ctoriginStack) { // Assignment if ( this == &ctoriginStack ) // verify x not assigned to x return *this ; if ( this -> lmaxEleInStack < ctoriginStack . lmaxEleInStack ) { // if destination stack is smaller than delete [ ] this -> lpstack ; // original stack, delete dest and alloc this -> lpstack = // sufficient memory new long [ ctoriginStack . lmaxEleInStack ] ; assert ( this -> lpstack ) ; // assure new succeeded // reset stack size attribute this -> lmaxEleInStack = ctoriginStack . lmaxEleInStack ; } // copy original to destination stack for ( long i = 0 ; i < ctoriginStack . lmaxEleInStack ; i ++ ) *( this -> lpstack + i ) = *( ctoriginStack . lpstack + i ) ; this -> ltopOfStack = ctoriginStack . ltopOfStack ; // reset stack position attribute return *this ; } long cmstackPush (char lplaceInStack ) { // Push Method if ( ltopOfStack == lmaxEleInStack - 1 ) // stack is full can't add element return lfalse ; ltopOfStack ++ ; // acquire free slot *(lpstack + ltopOfStack ) = lplaceInStack ; // add element return ltrue ; // any number other than zero is true } long cmstackPop (char& lretrievedStackEle ) { // Pop Method if ( ltopOfStack < 0 ) { // stack has no elements lretrievedStackEle = -1 ; // dummy element return lfalse ; } lretrievedStackEle = *( lpstack + ltopOfStack ) ; // stack has element -- return it ltopOfStack -- ; // stack is pop'd return ltrue ; // any number other than zero is true } long cmstackLookAtTop (char& lretrievedStackEle ) { // Pop Method if ( ltopOfStack < 0 ) { // stack has no elements lretrievedStackEle = -1 ; // dummy element return lfalse ; } lretrievedStackEle = *( lpstack + ltopOfStack ) ; // stack has element -- return it return ltrue ; // any number other than zero is true } long cmstackHasAnEle (char& lretrievedTopOfStack ) { // Has element method lretrievedTopOfStack = ltopOfStack ; return ltopOfStack < 0 ? lfalse : ltrue ; // 0 - false stack does not have any ele } // 1 - true stack has at least one element long cmstackMaxNbrOfEle (char& lretrievedMaxStackEle ) { // Maximum element method lretrievedMaxStackEle = lmaxEleInStack ; // return stack size in reference var return ltrue ; // Return Maximum Size of Stack } } ; Thanks, Anthony.

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