Pointer arithmetic with arrays in C++

I have a little doubt what happens with this pointer, the code is as follows:

#include <iostream>
using namespace std;
void func(int *, int);

int main(int argc, char *argv[])
{
    int i, a[10]={1,2,3,2,5};
    func(a,4);              
    for(i=0; i<=4; i++)
        cout<<a[i]<<endl;
    return 0;
}

void func(int *b,int n)                                     
{
    int i;
    for(i=0; i<=n; i++)
    {        
       if(b[i]==2) {
         b=b+1;                 
         b[i]=b[i]*2;       
       }                            
    }   
}   

Precisely in this line of code, it is not very clear to me what is happening:

void func(int *b,int n)                                   
{
    int i;
    for(i=0; i<=n; i++)
    {        
        if(b[i]==2) {
           b=b+1;                 
           b[i]=b[i]*2;     
        }                           
    }
}   

In this line, when i=1, it's going to enter if because the value of b[1] is equal to 2, but, in this case, the Pointer still points to the value 0, right? or has it been moving?, because when I run the program, the first and second values do not change, but the third value that is 3 prints it as 6, when it should print 4, right?.

In short, these are the lines that are not very clear to me:

b=b+1;
b[i]=b[i]*2;

Scroll and assign the value to b[i]?