Create Array of Symbols

Create array of symbols

The original answer was written back in September '11, but, starting from Ruby 2.0, there is a shorter way to create an array of symbols! This literal:

%i[address city state postal country]

will do exactly what you want.

Using %i and %I symbol array literal

I'm having trouble finding what the %i does in relation to a symbol array.

It is an array literal for an array of symbols. It does the same thing in relation to symbol arrays as ' does to strings.

Is there a literal notation for an array of symbols?

Yes! This is possible now in Ruby 2.0.0. One way to write it is:

%i{foo bar}  # => [:foo, :bar]

You can also use other delimiters, so you could also write %i(foo bar) or %i!foo bar! for example.

This feature was originally announced here:

http://www.ruby-lang.org/zh_TW/news/2012/11/02/ruby-2-0-0-preview1-released/

It is mentioned in the official documentation of Ruby here:

http://ruby-doc.org/core/doc/syntax/literals_rdoc.html#label-Percent+Strings

How can I add operation symbols (+, *, -, /) to an array in Javascript

You simply need to add quote around the symbols as follows -

var operations = ['*', '+', '-', '/'];
console.log(operations);

function getRandom(){
  return operations[Math.floor(Math.random() * Math.floor(4))]
}
// To get a random symbol - 
console.log(getRandom())

// One way to use a random symbol in a given expression would be as -
const num1 = Math.floor(100*Math.random()), num2 = Math.floor(100*Math.random());

const expression = `${num1}${getRandom()}${num2}`
const result = eval(expression)
console.log(result)

Using an array of strings to implement a symbol table in C

Use descriptive names for identifiers, not cryptic short names (like s and str_id).
Avoid Systems Hungarian Notation (i.e. naming or prefixing identifiers after their type or what-they-are as opposed to what-they-mean).
- In your case, I assume str_id is an abbreviation for struct_id (or string_id) - which is a bad name because it's already immediately obvious that it's a struct (or contains a string).
- It was popular right until the 1990s when programmers started using more powerful editors and IDEs that kept track of variable types - it just isn't needed today.
Always check if a heap allocation succeeded or failed by comparing calloc and malloc's return values to NULL. This can be done with if( some_pointer ) abort().
- Don't use assert( some_pointer ) because assertions are only enabled in debug builds, use abort instead as it signifies abnormal program termination compared to exit.
Pass a size_t parameter so consumers can specify the size of the symbol table.
Quantities of objects held in memory should be expressed as size_t (e.g. array indexers). Never use int for this!
You need to put a semi-colon at the end of each struct definition.
Are you sure you want an array-of-pointers-to-structs and not just an array-of-structs? In this case you can use inline structs and use a single allocation for the array, instead of allocating each member separately.
Because you're performing custom allocation, you must also define a destructor function.

struct symbol_table_entry {
  char* symbolText;
  int   id;
};

struct symbol_table {
  size_t count;
  struct symbol_table_entry** entries;
};

struct symbol_table* create_symbol_table( size_t count ) {
    struct symbol_table* stt = malloc( sizeof(struct symbol_table) );
    if( !stt )
    {
        abort();
    }
    stt->count = count;
    stt->entries = calloc( count, sizeof(struct symbol_table_entry) );
    if( !stt->entries ) {
        free( stt );
        abort();
    }
    // Note that calloc will zero-initialize all entries of the array (which prevents debuggers showing garbage string contents) so we don't need to do it ourselves.
    return stt;
}

void destroy_symbol_table( struct symbol_table* stt, bool free_strings ) {
    if( stt->entries ) {
        if( free_strings ) {
            for( size_t i = 0; i < stt->count; i++ ) {
                free( stt->entries[i]->symbolText );
            }
        }
        free( stt->entries );
    }
    free( stt );
}