Multiplication of long long & float

general
1

Thi question appeared in recent atcoder contest…
question link:C - Multiplication 3
This question is basic problem but took much time to get it,can any one please tell the clear concept of solving this problem

2

for the same problem my code is giving wrong answer can anyone tell me the mistake, Thanks.

#include <boost/multiprecision/cpp_int.hpp>
using namespace boost::multiprecision;
using namespace std;

int main() {
long long A;
cin>>A;
float B;
cin>>B;
B=B*(100);
long long C=B;
long long ans=(A)*C;
ans=ans/100;
cout<<ans<<"\n";
return 0;
}

3 
#include <cstdio>
#include <cmath>

using namespace std;

long long A, B;
int b1, b2;
long long ans;

int main() {
    scanf("%lld%d.%d", &A, &b1, &b2);
    B = b1 * 100 + b2;
    ans = (long long) (A * B) / 100;
    printf("%lld\n", ans);
    return 0;
}

This is the code in C++
You need to use long long in Cpp or long/BigInteger in JAVA
Please like

4 
import java.math.BigDecimal;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long A = sc.nextLong();
        double B = sc.nextDouble();
        BigDecimal a = new BigDecimal(String.valueOf(A));
        BigDecimal b = new BigDecimal(String.valueOf(B));
        BigDecimal result = a.multiply(b);
        System.out.println(result.longValue());
    }
}

This is JAVA please like

5

Consider the test input:

873938008102648 4.43
1 Like
6

Oh ok i guess it’s because of that precision case right ? i mean we cant compare float number due to that slight plus minus. Like here 423.0 is not 432 its 432(+) or (-) x(for some small x).
If i am wrong please correct me.

7

Well no concept is required. Do as it is said, but take care of the precision. Here’s my code-

#include<bits/stdc++.h>
#define ll long long int
using namespace std;
int main(){
       ll a;
       long double b;
       cin>>a>>b;
       ll ans;
       ans=a*b;
       cout<<ans;
}
8

Thanks,but I have done same way it giving WA in first testcase of atcoder,dont know why???
try to submit again…u will know

9

if we use long long for A and long double for B is it enough??i am getting WA for that too… then what is the logic??

11

I did this and got AC

#include <boost/multiprecision/cpp_int.hpp>
using namespace boost::multiprecision;
using namespace std;

int main() {
long long A;
cin>>A;
float B;
cin>>B;
B=B*(100);
long long C=(long long)round(B);
long long ans=(A)*C;
ans=ans/100;
cout<<ans<<"\n";
return 0;
}