Question

In most languages, by declaring the type of a variable in a program in advance, the compiler can obtain a lot of information about the variable required when generating code through such a declaration. Describe the information that the compiler can get through this type declaration and what it does using this information (for example, performing type checking to find a type-error is one of these things).

Answer 1

There are generally three types of compilers.

1. Single Pass Compilers.

2. Two Pass Compilers.

3. Multipass Compilers.

Which means in Single Pass Compilers, the source code is directly transformed into machine code. But Two pass compilers have two ends, generally a front end and a back end.

And, finally the multipass compiler processes source code of a program several times. Which makes it to require less memory.

Coming to the modern Compilers. Now if we declare the type of a variable in a program in advance makes us to:

• Identify functions to get implemented on that datatype. For example, if it is string, then it shows functions such as length, find, upper casing, lower casing etc., if it is a list, then it shows functions such as length, append, sort etc.
• Another use of declaring in advance is, when we do arithmetic operations on two different datatypes such as int and float or int and double, it shows error in compiler itself.
• Problems like run time errors can be identified even before compiling when we declare data types in advance.
• Even it shows exceptions to handle, that is if we do division between two numbers which may consist zero, so it shows to keep an exception handler (try block) and handle all those exceptions.
• If we declare variables and if they aren’t used, then it will be garbage collected. And even processes such as type casting and type conversion will be easy.

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