I am new to posting and relatively new to coding in c++.
My question involves:
Handling decimal values in evaluating postfix using stacks in c++. This is a homework assignment, but I have already gotten my code to work for the basic requirement. I am not asking for help with my homework. My professor wants us to brute force the assignment, so I have avoided many shortcuts using special header files such as <stack>.
I have researched the question and was not satisfied with the answers given. No one else seems to have split up their code like mine. I am having an issue passing a value from the inner loop which detects the decimal values to the rest of the main function. The code compiles and runs, but my final result is gibberish. I found a post which states multiple values cannot be passed from a function with 'return', but I do need at least two values returned from the inner decimal function. I do not understand the 'tuple' or 'pair' commands.
I know this is a wordy prelude, but I do want any readers to understand I have read pre-requisite materials and did lost of research. Personally, I hate brute force methods. I understand that a response may not be in time to help with my project, but I have been working on this for weeks. I would like to get the satisfaction of seeing this method work as conceived. Suggestions and pointers are very much welcome.
Here is the link to my code:
link
Here is my code:
//*****************************************************************************
// Postfix expression evaluation
// 11/13/2012
// by DJH
//
// all applicable copyrights apply
//
// this program evaluates an input postfix string
//
// created using Dev-C++ 5.2.0.3
//*****************************************************************************
// ----------------------------------libraries---------------------------------
#include <iostream> // For cin, cout and endl
#include <string>
#include <cctype>
#include <vector>
#include <sstream>
#include <cstdlib>
#include <cmath>
#include <iomanip>
using namespace std;
// ------------------------------ Globals -------------------------------------
string postfix;
// --------------------------- stack class ------------------------------------
class Stack {
public:
enum {MaxStack = 50};
void init() {top = -1;}
void push( double p ) {
if ( isFull() ) {
cerr << "Full Stack. DON'T PUSH\n";
return;
}
else {
arr[ ++top ] = p;
cout << "Just pushed " << p << endl;
return;}
}
int pop() {
if (isEmpty() ) {
cerr << "\tEmpty Stack. Don't Pop\n\n";
return 1;
}
else
return arr[top--];
}
bool isEmpty() {return top < 0 ? 1 : 0;}
bool isFull() {return top >= MaxStack -1 ? top : 0;}
void dump_stack() {
cout << "The Stack contents, from top to bottom, from a stack dump are: " << endl;
for (int s = top; s >= 0; s--)
cout << "\t\t" << arr[s] << endl;
}
private:
int top;
double arr[MaxStack];
} pStack;
// ------------------------------ end stack class -----------------------------
// -----------------------------function prototypes----------------------------
void evalPostfix( string);
double decimalEvaluate( string, int, double);
// ----------------------------------------------------------------------------
// -----------------------------------Main()-----------------------------------
int main() {
cout << "Enter a postfix expression\n\t (without spaces - using '_' for delimiters):\n\t";
cout << "For example: 8_5_3_+_*_2_/_5_+\n" << endl;
getline(cin, postfix);
// postfix = "7_2_*_5_+_2_*";
cout << "You entered: " << postfix << endl;
int c = 0;
while (postfix[c] != '\0') {
// this loop counts the characters in the input string including
// whitespace
++c;
}
cout << "\tThe string length is:\t" << c << endl;
evalPostfix(postfix);
int result = pStack.pop();
cout << "The result of the postfix expression is: " << result << endl;
/*
stack commands:
Stack a_stack; // creates new stack
a_stack.init(); // initializes top element
a_stack.pop(); // pops top of stack
a_stack.push(n); // push element to top of stack
a_stack.dump_stack(); // displays the contents of the stack from top to bottom
*/
return 0;
cin.get();
}
// --------------------------------end of Main()-------------------------------
// ------------------------------functions follow------------------------------
void evalPostfix( string) {
double ch = 0, dc = 0, b = 0, a = 0, d = 0;
double tempDC = 0;
double tempDCD = 0;
char op;
int i = 0, j = 0, k = 0, m = 0, n = 0, q = 0;
while (postfix[i] != '\0') {
if (postfix[i] == '_') {
i++;
} else if (isdigit(postfix[i])) {
ch = postfix[i] - '0'; // for numbers only
j = i + 1;
while (postfix[j] != '_') {
if (isdigit(postfix[j])) {
ch = ch * 10 + (postfix[j] - '0');
k = j + 1;
// this accounts for decimals by skipping the '.' and
// conducting operations on trailing numbers
if (postfix[k] == '.') {
dc = 0;
decimalEvaluate(postfix, k, dc);
dc = tempDC / tempDCD;
d = ch + dc;
k++;
}
j = k - 1;
j++;
}
}
cout << "Post decimal function k: " << k << endl;
cout << "Post decimal function dc: " << setprecision(12) << dc
<< endl;
cout << "Post decimal function d: " << d << endl;
pStack.push(d);
i = j - 1;
i++;
} else if (postfix[i] == '+' || postfix[i] == '-' || postfix[i] == '*'
|| postfix[i] == '/' || postfix[i] == '^') {
b = pStack.pop();
a = pStack.pop();
op = postfix[i]; // for operators only
switch (op) {
case '+':
pStack.push(a + b);
break;
case '-':
pStack.push(a - b);
break;
case '*':
pStack.push(a * b);
break;
case '^':
pStack.push(pow(a, b));
break;
case '/':
if (b == 0) {
cout << "Division by zero not allowed!" << endl;
cin.get();
exit(0);
}
pStack.push(a / b);
default:
cout << "Invalid Operation" << endl;
}
i++;
}
}
}
// ----------------------------------------------------------------------------
double decimalEvaluate(string postfix, int k, double dc) {
dc = 0;
double tempDC = 0;
double tempDCD = 0;
int n = 0, m = 0, lenDC = 0;
n = k;
while (postfix[n] != '_') {
if ((isdigit(postfix[n])) == false) {
n++;
}
cout << "This step (1) n: " << n << endl;
if (isdigit(postfix[n])) {
m = n;
// assumes characters between a '.' and '_' are all digits
// (may need to check)
while (postfix[m] != '_') {
lenDC++;
// this loop counts the digits in the input trailing a decimal
// point
m++;
}
cout << "This step (2) m: " << m << endl;
cout << "This step (2) lenDC: " << lenDC << endl;
while ((postfix[n]) != '_') {
tempDC = tempDC * 10 + (postfix[n]) - '0';
n++;
}
cout << "This step (3) n: " << n << endl;
cout << "This step (3) tempDC: " << tempDC << endl;
}
k = n;
tempDCD = pow(10, lenDC);
dc = tempDC / tempDCD;
cout << "This step (4) k: " << k << endl;
cout << "This step (4) tempDCD: " << tempDCD << endl;
cout << "This step (4) tempDC: " << tempDC << endl;
cout << "This step (4) dc: " << dc << endl;
}
return dc, k, tempDC, tempDCD;
}
Pass the variables by reference: