#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>

// Global variables
sem_t mutex, writeMutex;
int data = 0, readers = 0;

void* reader(void* arg) {
    while (1) {
        sem_wait(&mutex);
        readers++;
        if (readers == 1) {
            sem_wait(&writeMutex);
        }
        sem_post(&mutex);

        // Reading data
        printf("Reader %d read: %d\n", *((int*)arg), data);

        sem_wait(&mutex);
        readers--;
        if (readers == 0) {
            sem_post(&writeMutex);
        }
        sem_post(&mutex);

        // Sleep to simulate reading time
        usleep(100000);
    }
    return NULL;
}

void* writer(void* arg) {
    while (1) {
        sem_wait(&writeMutex);

        // Writing data
        data++;
        printf("Writer %d wrote: %d\n", *((int*)arg), data);

        sem_post(&writeMutex);

        // Sleep to simulate writing time
        usleep(1000000);
    }
    return NULL;
}

int main() {
    int num_readers = 3;
    int num_writers = 2;
    
    sem_init(&mutex, 0, 1);
    sem_init(&writeMutex, 0, 1);

    pthread_t readers[num_readers], writers[num_writers];
    int readerIDs[num_readers], writerIDs[num_writers];

    for (int i = 0; i < num_readers; i++) {
        readerIDs[i] = i;
        pthread_create(&readers[i], NULL, reader, &readerIDs[i]);
    }

    for (int i = 0; i < num_writers; i++) {
        writerIDs[i] = i;
        pthread_create(&writers[i], NULL, writer, &writerIDs[i]);
    }

    for (int i = 0; i < num_readers; i++) {
        pthread_join(readers[i], NULL);
    }

    for (int i = 0; i < num_writers; i++) {
        pthread_join(writers[i], NULL);
    }

    sem_destroy(&mutex);
    sem_destroy(&writeMutex);

    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
}