Final answer:
The main difference is that ML let constructs create immutable bindings and have different scoping rules, while C block variables are mutable and localized to the block they are declared in.
Step-by-step explanation:
The difference between the names defined in an ML let construct and the variables declared in a C block primarily lies in their immutability and scope. In ML, a functional programming language, the let construct is used to bind values to names. The key characteristic of these bindings is that they are immutable, meaning once a name is assigned a value, it cannot be changed. For example, the following ML code segment creates an immutable binding: let val x = 5 in x + x end;.
On the other hand, variables declared in a C block, a procedural programming language, are mutable. This means their values can be altered throughout their scope. C blocks define the variable's scope and lifetime, typically bracketed by curly braces {}. For instance, int x = 5; x = x + 1; shows a variable x being modified within its scope.