Why the first line of output is 2*1=0

Question

#include <iostream>
using namespace std;

int main()
{
int a=1,b;
while(a<=10)
{
cout<<"2*"<<a<<"="<<b<<endl;
a=++a;
b=2*a;
}

}
Output:
2*1=0
2*2=4
2*3=6
2*4=8
......

Why 2*1=0

Answer 1

Variable <b> is uninitialised in the first round of the loop. You need to move assignment of <b> before printing output.

Uninitialised variables have arbitrary value.

while(a <= 10)
{
b = 2 * a;
cout << "2*" << a << "=" << b << endl;
++a;
}