mutex_sample.cpp

#include <thread>
#include <stdio.h>
#include <mutex>

int count = 0;
std::mutex writer;

void counter(){
    for (int i=0; i < 100000; ++i){
        writer.lock();
        count++;
        writer.unlock();
    }
}

int main(){
    std::thread counter1(counter);
    std::thread counter2(counter);
    counter1.join();
    counter2.join();
    printf("Final count is %d\n", count);
}

Compile and Run:
g++ -Wall -std=c++11 mutex_sample.cpp -o mutex.o; ./mutex.o