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Pre Evaluation

The document contains a C++ program that defines a Stack class for evaluating prefix expressions. It allows the user to input a prefix expression, processes it by reversing the string, and evaluates it using a stack data structure. The program handles basic arithmetic operations and checks for division by zero errors.

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16 views4 pages

Pre Evaluation

The document contains a C++ program that defines a Stack class for evaluating prefix expressions. It allows the user to input a prefix expression, processes it by reversing the string, and evaluates it using a stack data structure. The program handles basic arithmetic operations and checks for division by zero errors.

Uploaded by

waaasimfke
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOCX, PDF, TXT or read online on Scribd
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#include <iostream>

#include <cstring>

#include <cmath>

using namespace std;

class Stack {

private:

char expr[100];

int arr[100];

int top;

public:

Stack() {

top = -1;

void input() {

cout << "Enter the prefix expression: ";

cin.getline(expr, 100);

strrev(expr); // Reverse the expression for processing

void push(int num) {

arr[++top] = num;

int pop() {

return arr[top--];

}
int evaluate() {

int i = 0;

while (expr[i] != '\0') {

if (expr[i] == ' ') {

i++;

continue;

if (isdigit(expr[i])) {

int num = 0, j = i;

while (isdigit(expr[j])) j++; // Find the length of the number

for (int k = j - 1; k >= i; k--) {

num = num * 10 + (expr[k] - '0'); // Convert to integer

i = j; // Move the index to next character after the number

push(num);

} else {

char ch = expr[i];

int a = pop();

int b = pop();

switch (ch) {

case '+':

push(a + b);

break;

case '-':

push(a - b);

break;

case '/':
if (b == 0) {

cout << "Division by zero!" << endl;

return -1;

push(a / b);

break;

case '*':

push(a * b);

break;

case '^':

push((int)pow(a, b));

break;

default:

cout << "Invalid operator" << endl;

return -1;

i++;

return pop();

};

int main() {

Stack obj;

obj.input();

int res = obj.evaluate();

cout << "The result of the prefix expression is: " << res << endl;

return 0;
}

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