Đổi nhị phân

#include<iostream>
#include<cstdio>
#include<vector>

using namespace std;

vector <char> v;
int i=0;
void doctep(long &n){
    FILE *fp;
    fp = fopen("input3.txt", "r");
    fscanf(fp, "%d", &n);
}

char *doinhiphan(long n){
    char s[100005];
    while(n > 0){
        int t=n%2;
        s[i++] = t + '0';
        n/=2;
    }
    return s;
}

void in(char s[]){
    for(int j=0; j<i; j++){
        cout<<s[j];
    }
}

main(){
    long n;
    char s[100005];
    doctep(n);
    cout<<doinhiphan(n);
    in(s);
}