How do i write nested if statement?

So i want to make a simple if statement like this :

if(a=1)
{
    if(variable1=1)
    {
        cout<<"a1=1";
    }
    else
    {
        cout<<"error";
    }
}

if(a=2)
{
    if(variable1=1)
    {
        cout<<"a2=1"
    }
    else
    {
        cout<<"error";
    }
}

Problem :
When i set a to 2 and variable1 to 1 it will just print a1=1 not a2=1. How do i fix this?
Sorry if there is a miss-writing, or bad english in this post. I hope someone answers…

comparison
cout
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>Solution :

You are using the assignment operator(=) instead of the comparison operator (==). The assignment operator will always return true if the assignment is successful, hence it is going in the first if statement.

To solve the issue, change = to == in your code.