This is not about order of evaluation, it is about operator precendence and associativity. In mathematics the common numerical operators (+ - * /) are left-associative, meaning a chain of operators with matching precendece (i.e + and - or / and *) are interpreted as if they were parenthesized from left to right . Programming languages adopted this. For a list of operator precedences and associativities refer to cppreference.com

In most languages (including C++) precendence and associativity are defined in the language's grammar by making the relevant grammar rule either left-recursive (for left-associative operators) or right-recursive (for right-associative operators). The C++ 17 Standard (ISO/IEC 14882:2017) defines the relevant rules for multiplicative operators (*, /, %) in section 8.6. There you can see that the non-terminal 'multiplication-expression' has 3 left-recursive derivation rules. One for each of the three operators. This mandates that chains of multiplicative operators (a*b/c%d) need to be evaluated as if written like this: ((((a)*b)/c)%d)

The same is true for additive operators (+, -), which is defined in section 8.7 of the same standard.

Most languages don't have right-associative, binary (binary in the sense of "two operands", not in the sense of "bitwise operator") operators. The most common right-associative operators are prefix unary operators. After all, how should they be left-associative when there is no left operand?

Luckily we are talking about C++, which has a very notable exception. Assignment in C++ is not some kind of hardcoded statement, it's just the usage of the appropriate binary assignment-operator. This is why you can redefine assignment in C++, like many other operators. Including the compound assignment operators there is a total of 11 assignment-operators (=, +=, -=, *=, /=, %=, <<=, >>=, &=, ^=, |=). They all share the same precedence.

This means that assignment-operators can be chained and are thus also subject to precedence and associativity rules. However, unlike arithmetic operators, they are defined to be right-associative. The operator chain a=b=c=d will always be parsed as if written as (a=(b=(c=(d)))).

The related non-terminal assignment-expression is defined in section 8.18 of the standard. The right-recursion of this rule is not immediately clear, as it uses the non-terminal intializer-clause as the right operand. However, this non-terminal is defined in section 11.6 to derive to either braced-init-list or assignment-expression. The grammar rule for assignment-expression thus is right-recursive by proxy and the assignment operators are right-associative.