Why answer of this code is 8?

Question

#include <iostream>
using namespace std;
int main()
{ int a=0;
a=1<<3;
cout<<a;
return 0;
}

Answer 1

because 1 = 0001.
And your bitshift pushed the 1, 3 times to the left.
8 = 1000.

Answer 2

This is called bitwise operator, 1<<3 mean move 3 spaces to left the bit.
1 - Original
10 - One moved
100 - Two moved
1000 - Three moved.

Now by default when printed on scren is showed on decimal, this mean you need transform from binary to decimal.
2^3 = 8

Extra: Bitwise accept number input on decimal also: Check if you want to eval:
a = 4<<3
You need first param in binary this mean
a = 100<<3
Now move three spaces to left
a = 100 000
a = 2^5 = 32

Hope it helps.