CPP: threading in LINUX showing output

#include <iostream>
#include <thread>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <future>
#include <functional>

void bar(std::future<int>& fut){

//get the promised variable
//allocate memory for buffer

int len = fut.get(); //get variable
char * buff; //create buffer
buff = (char*) malloc (len+1); //allocate memory

if(buff==NULL){
//exit if no allocation
exit(1);
}
for(int n=0;n<len;n++){
buff[n]=rand()%26+'a';
}
buff[len]='\0';

std::cout<<"\nvalue: "<<buff<<'\n';
free(buff); //free memory
}

void foo(){
//get integer
       //create promise
//engage future
//send future to new thread

std::promise<int> malin; //create promise
std::future<int> fut = malin.get_future(); //engage, make it so!
std::thread th1 (bar, std::ref(fut)); //send future to thread

int i,n;

std::cout<<"How long do you want the string? "<<'\n';
std::cin>>i;

//set value of promised integer

malin.set_value(i); //fulfill promise
th1.join(); //join thread with foo
}

int main(){

//spawn new thread calling foo()
//pause intil thread complete

std::thread t1(foo); //launch thread
        t1.join(); //join thread with main
        return 0;
}
OUTPUT