#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// Define maximum size for the stack.
#define MAX 100

// Struct for the stack.
typedef struct {
    int top;
    char items[MAX];
} Stack;

// Function to initialize the stack.
void initStack(Stack *s) {
    s->top = -1;
}

// Function to check if the stack is empty.
int isEmpty(Stack *s) {
    return s->top == -1;
}

// Function to push an element to the stack.
void push(Stack *s, char value) {
    if (s->top < MAX - 1) {
        s->items[++s->top] = value;
    } else {
        printf("Stack is full!\n");
    }
}

// Function to pop an element from the stack.
char pop(Stack *s) {
    if (!isEmpty(s)) {
        return s->items[s->top--];
    } else {
        return '\0'; // Return null character if stack is empty.
    }
}

// Function to check the precedence of operators.
int precedence(char op) {
    switch (op) {
        case '+':
        case '-':
            return 1;
        case '*':
        case '/':
            return 2;
        case '%':
            return 3;
        case '(':
            return 0;
    }
    return -1; // Return -1 for invalid operators.
}

// Function to convert infix expression to postfix expression.
char* infixToPostfix(char* infix) {
    static char postfix[MAX];
    int i, j=0;
    Stack s;
    initStack(&s);

    for (i = 0; infix[i] != '\0'; i++) {
        if (infix[i] == '(') {
            push(&s, infix[i]);
        } else if (infix[i] == ')') {
            while (!isEmpty(&s) && s.items[s.top] != '(') {
                postfix[j++] = pop(&s);
            }
            pop(&s); // Remove the opening parenthesis '(' from the stack.
        } else if (infix[i] == '+' || infix[i] == '-' || infix[i] == '*' || infix[i] == '/' || infix[i] == '%') {
            while (!isEmpty(&s) && precedence(infix[i]) <= precedence(s.items[s.top])) {
                postfix[j++] = pop(&s);
            }
            push(&s, infix[i]);
        } else {
            postfix[j++] = infix[i];
        }
    }

    while (!isEmpty(&s)) {
        postfix[j++] = pop(&s);
    }

    postfix[j] = '\0'; // Null terminator for the string.
    return postfix;
}

int main() {
    char P[] = "(A-(B/C)*D+E)*F%G";
    char* Q;

    Q = infixToPostfix(P);

    printf("Infix expression: %s\n", P);
    printf("Postfix expression: %s\n", Q);

    return 0;
}
by

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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
}