#include <iostream>
#include <cmath> // Include cmath for rounding

using namespace std;

// Define the maximum size of the stack
const int MAX_SIZE = 100;

// Define a stack class using an array
class Stack {
public:
    Stack() {
        top = -1;
    }

    bool isEmpty() {
        return top == -1;
    }

    bool isFull() {
        return top == MAX_SIZE - 1;
    }

    void push(char c) {
        if (!isFull()) {
            stackArray[++top] = c;
        }
    }

    char pop() {
        if (!isEmpty()) {
            return stackArray[top--];
        }
        return '\0'; // Return null character if the stack is empty
    }

    char peek() {
        if (!isEmpty()) {
            return stackArray[top];
        }
        return '\0'; // Return null character if the stack is empty
    }

private:
    char stackArray[MAX_SIZE];
    int top;
};

// Function to perform arithmetic operations
double performOperation(double operand1, double operand2, char op) {
    switch (op) {
        case '+':
            return operand1 + operand2;
        case '-':
            return operand1 - operand2;
        case '*':
            return operand1 * operand2;
        case '/':
            if (operand2 != 0) {
                return operand1 / operand2;
            } else {
                cout << "Error: Division by zero" << endl;
                exit(1);
            }
        default:
            cout << "Error: Invalid operator" << endl;
            exit(1);
    }
}

// Function to check if a character is a digit
bool isDigit(char c) {
    return c >= '0' && c <= '9';
}

// Function to calculate the length of a C-style string
int stringLength(const char* str) {
    int length = 0;
    while (str[length] != '\0') {
        length++;
    }
    return length;
}

// Function to evaluate an expression using the PEMDAS rule
double evaluateExpression(const char* expression) {
    Stack operandStack;
    Stack operatorStack;
    int length = stringLength(expression);

    for (int i = 0; i < length; i++) {
        char currentChar = expression[i];

        if (isDigit(currentChar)) {
            double operand = currentChar - '0';
            while (i + 1 < length && (isDigit(expression[i + 1]) || expression[i + 1] == '.')) {
                if (isDigit(expression[i + 1])) {
                    operand = operand * 10 + (expression[i + 1] - '0');
                } else if (expression[i + 1] == '.') {
                    double decimalFactor = 0.1;
                    while (i + 2 < length && isDigit(expression[i + 2])) {
                        operand += (expression[i + 2] - '0') * decimalFactor;
                        decimalFactor *= 0.1;
                        i++;
                    }
                }
                i++;
            }
            operandStack.push(operand);
        } else if (currentChar == '(') {
            operatorStack.push(currentChar);
        } else if (currentChar == ')') {
            while (!operatorStack.isEmpty() && operatorStack.peek() != '(') {
                char op = operatorStack.pop();
                double operand2 = operandStack.pop();
                double operand1 = operandStack.pop();
                double result = performOperation(operand1, operand2, op);
                operandStack.push(result);
            }
            operatorStack.pop(); // Pop the '('
        } else if (currentChar == '+' || currentChar == '-' || currentChar == '*' || currentChar == '/') {
            while (!operatorStack.isEmpty() && operatorStack.peek() != '(' &&
                   ((currentChar == '+' || currentChar == '-') && (operatorStack.peek() == '*' || operatorStack.peek() == '/'))) {
                char op = operatorStack.pop();
                double operand2 = operandStack.pop();
                double operand1 = operandStack.pop();
                double result = performOperation(operand1, operand2, op);
                operandStack.push(result);
            }
            operatorStack.push(currentChar);
        }
    }

    while (!operatorStack.isEmpty()) {
        char op = operatorStack.pop();
        double operand2 = operandStack.pop();
        double operand1 = operandStack.pop();
        double result = performOperation(operand1, operand2, op);
        operandStack.push(result);
    }

    return operandStack.pop();
}

int main() {
    char expression[MAX_SIZE];
    cout << "Enter a math expression: ";
    cin.getline(expression, MAX_SIZE);
    double result = evaluateExpression(expression);
    cout << "Result: " << result << endl;
    return 0;
}

C++ Online Compiler

Write, Run & Share C++ code online using OneCompiler's C++ online compiler for free. It's one of the robust, feature-rich online compilers for C++ language, running on the latest version 17. Getting started with the OneCompiler's C++ compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as C++ and start coding!

Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

#include <iostream>
#include <string>
using namespace std;

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}