Procedural Programming + Ada, Lesson 3 – Imperative Syntax

To facilitate the creation and management of separate code files for each example, we will set up the project and use gprbuild instead of the gnatmake compiler. Here I will create a folder called learn-ada in Documents with the following structure:

The learn_ada.gpr file is a declaration like the package.json of NodeJS -based project , but has a much simpler structure:

• We have languages ​​that can be used in the project ada and c .
• All directories containing the code that we write will be placed in the src directory.
• The program will start from the main.adb file located at the first level right in the src directory.
• The example comment lines for declaring additional use of a library that we write compiled into executables, include: directory name, library name, compiled library type called Dynamic .
• The directory containing the executables after compilation is complete is obj .

Now we need to copy/paste the code of the Hello World program:

In the command line, navigate to the working directory of Documents/learn-ada .

Then run the compile command using the gprbuild project manager and continue to run the main executable generated by gprbuild in the obj directory.

Running the compile command and the main file will stay this way because we’ve set up the gpr file to automatically find all the code files in the src directory. In the examples from here on, I will only copy/paste the result of running the main file to reduce unnecessary iterations. And now we’ll go through all the common imperative syntaxes.

Declare variable

The beginning is the operation of variable declaration and value assignment. We have variable names named in the form of sub-program and package , with the first letter of each word capitalized and words joined by an underscore _ .

Ada ‘s variable data type syntax is a descriptor suffix similar to Scala , TypeScript , Kotlin , etc.. The variable name is followed by : Tên_Kiểu_Dữ_Liệu . And the assignment operation uses the := notation like SQL instead of the = notation like most other languages.

Since we haven’t touched the standard libraries yet, we’ll keep in mind that the string concatenation is & . Accompanied by the operation to convert integer N to string type is Integer'Image (N) . Compared to C , the variable declaration part is defined by Ada in its own area by the structure of the syntax. When writing programs in C , the habit of good dev to pass on is to focus on declaring in the first lines of sub-program .

If.. Then.. Else

Ada ‘s serial if .. else syntax is also very familiar compared to other Imperative languages. Here we have the word then used to end the conditional expression and in the next part else if is written as elsif phonetically.

By the way, we learned more about the Put (String) unbroken string printing operation and the Get (N) operation to read the user input and write to the N variable. Conditional tests used in the example include:

• Check for equivalence value = .
• The or keyword is equivalent to the symbol || in C and JavaScript that we already know.
• The in test looks for an element that belongs to a certain set of values.

Indeed, in terms of high-level programming interface criteria, Ada is much more user-friendly than C If you notice, Ada ‘s built-in procedures all have very clear and complete names, not abbreviations like sub-program in the C standard library. For example, C ‘s any type-to-integer converter is named atoi() – if fully understood, any_to_integer .

The story is that the C compiler will not automatically optimize the source files we write. That’s why when C was originally designed to communicate at a contiguous level with the resources of low-level programming systems, people always tried to minimize identifier names in the manipulation of naming variables and sub-program . Perhaps that’s why C is powerful, but using C for general applications is very difficult compared to high-level programming languages. And Ada , was probably made to perfect C in this respect.

Case .. When

Instead of switch .. case we have case .. when which is very similar to SQL :

Oh.. the or in this syntax is replaced by the | . symbol . I tried using this notation in place of or in the if .. else syntax, and I got an error. This is a point that we may need to keep in mind now and forever.

Ternary Operator

In addition to the branching command structures, in C and JavaScript we also have Ternary Operator conditional expressions to test a condition and select the value assigned to the variable.

If first > second then choose first to assign to which , otherwise choose second . And in some other languages ​​the symbols ? and : will be replaced by keywords with clearer meanings. And if so, then Ada will definitely use the keywords, in the previous post they clearly introduced that.

The Elm language introduced in the previous Sub-Series also had a similar if .. else conditional expression. However, the difference is that in Ada we will need to use a pair of parentheses () to enclose this expression. Probably because it’s easier to separate information when reading a long statement with elements separated by a space.

Loops

Compared to the popular Imperative languages, Ada does not have a do .. while syntax, but instead has a bare-loop with no limit of iterations. Here we will have to insert a statement that checks the condition and exits the loop at some point:

• loop – the keyword that starts the loop
• exit when .. ; – statement that checks the condition to exit the loop
• end loop; – loop end keyword

The for .. in loop syntax is quite similar to JavaScript ‘s for .. in/of syntax.

And the while loop syntax is also very familiar.

Next we will talk about sub-program ..

(unpublished) [Procedural Programming + Ada] Lesson 4 – Package & Sub-Program