03-types.adoc

Basic data types

Integers

As seen in the previous chapter, integers are numbers which are written without a fractional component and without a decimal point.

For example: 32, -174, 0, 10_000_000 are all integers. Notice that we can use _ as a thousands separator, to make larger numbers more readable (it is easier to see that we’re talking about 10 million when it’s written as 10_000_000 rather than as 10000000).

The usual mathematical operators — addition (+), subtraction (-), multiplication (*), and division (/) — work as one would expect. The first three operations always produce integers, while dividing two integers always gives a floating point number (a number with a decimal point) as a result, even if two numbers can be divided without a remainder.

Integer division (division where the fractional part is discarded) can be achieved with the div operator. An operator mod is used if one is interested in the remainder (modulus) of an integer division. The result of these two operations is always an integer.

integers.nim

link:{source-dir}/integers.nim[role=include]

1. The echo command will print to the screen everything that follows it separated by commas. In this case, it first prints the string a + b = , and then after it, in the same row, it prints the result of the expression a + b.

We can compile and run the above code, and the output should be:

a + b = 15
a - b = 7
a * b = 44
a / b = 2.75
a div b = 2
a mod b = 3

Floats

Floating-point numbers, or floats for short, are an approximate representation of real numbers.

For example: 2.73, -3.14, 5.0, 4e7 are floats. Notice that we can use scientific notation for large floats, where the number after the e is the exponent. In this example, 4e7 is a notation representing 4 * 10^7.

We can also use the four basic mathematical operations between two floats. Operators div and mod are not defined for floats.

floats.nim

link:{source-dir}/floats.nim[role=include]

c + d = 9.0  (1)
c - d = 4.5
c * d = 15.1875
c / d = 3.0  (1)

1. Notice that in the addition and division examples, even though we get a number without a decimal part, the result is still of the floating type.

The precedence of mathematical operations is as one would expect: multiplication and division have higher priority than addition and subtraction.

echo 2 + 3 * 4
echo 24 - 8 / 4

14
22.0

Converting floats and integers

Mathematical operations between variables of different numerical types are not possible in Nim, and they will produce an error:

let
  e = 5
  f = 23.456

echo e + f   # error

The values of variables need to be converted to the same type. Conversion is straight-forward: to convert to an integer, we use the int function, and to convert to a float the float function is used.

let
  e = 5
  f = 23.987

echo float(e)      (1)
echo int(f)        (2)

echo float(e) + f  (3)
echo e + int(f)    (4)

1. Printing a float version of an integer e. (e remains of integer type)

2. Printing an int version of a float f.

3. Both operands are floats and can be added.

4. Both operands are integers and can be added.

5.0
23
28.987
28

Note	When using the int function to convert a float to an integer no rounding will be performed. The number simply drops any decimals. To perform rounding we must call another function, but for that we must know a bit more about how to use Nim.

Characters

The char type is used for representing a single ASCII character.

Chars are written between two single ticks ('). Chars can be letters, symbols, or single digits. Multiple digits or multiple letters produce an error.

let
  h = 'z'
  i = '+'
  j = '2'
  k = '35' # error
  l = 'xy' # error

Strings

Strings can be described as a series of characters. Their content is written between two double quotes (").

We might think of strings as words, but they can contain more than one word, some symbols, or digits.

strings.nim

link:{source-dir}/strings.nim[role=include]

1. An empty string.

2. This is not a number (int). It is inside double quotes, making it a string.

3. Even though this is only one character, it is not a char because it is enclosed inside of double quotes.

Special characters

If we try to print the following string:

echo "some\nim\tips"

the result might surprise us:

some
im	ips

This is because there are several characters which have a special meaning. They are used by prepending the escape character \ to them.

• \n is a newline character

• \t is a tab character

• \\ is a backslash (since one \ is used as the escape character)

If we wanted to print the above example as it was written, we have two possibilities:

• Use \\ instead of \ to print backslashes, or

• Use raw strings which have syntax r"…​" (putting a letter r immediately before the first quote), in which there are no escape characters and no special meanings: everything is printed as it is.

echo "some\\nim\\tips"
echo r"some\nim\tips"

some\nim\tips
some\nim\tips

There are more special characters than the ones listed above, and they are all found in the Nim manual.

String concatenation

Strings in Nim are mutable, meaning their content can change. With the add function we can add (append) either another string or a char to an existing string. If we don’t want to change the original string, we can also concatenate (join together) strings with the & operator, this returns a new string.

stringConcat.nim

link:{source-dir}/stringConcat.nim[role=include]

1. If we plan to modify strings, they should be declared as var.

2. Adding another string modifies the existing string p in-place, changing its value.

3. We can also add a char to a string.

4. Concatenating two strings produces a new string, without modifying the original strings.

p is now: abcdef
q is now: xyz
concat: abcdefxyz
p is still: abcdef
q is still: xyz

Boolean

A boolean (or just bool) data type can only have two values: true or false. Booleans are usually used for control flow (see next chapter), and they are often a result of relational operators.

The usual naming convention for boolean variables is to write them as a simple yes/no (true/false) question, e.g. isEmpty, isFinished, isMoving, etc.

Relational operators

Relational operators test the relation between two entities, which must be comparable.

To compare if two values are the same, == (two equal signs) is used. Do not confuse this with =, which is used for assignment as we saw earlier.

Here are all the relational operators defined for integers:

relationalOperators.nim

link:{source-dir}/relationalOperators.nim[role=include]

g is greater than h: false
g is smaller than h: true
g is equal to h: false
g is not equal to h: true
g is greater or equal to h: false
g is smaller or equal to h: true

We can also compare characters and strings:

relationalOperators.nim

link:{source-dir}/relationalOperators.nim[role=include]

1. All uppercase letters come before lowercase letters.

2. String comparison works char-by-char. First three characters are the same, and character b is smaller than character z.

3. String length doesn’t matter for comparison if their characters are not identical.

4. Shorter string is smaller than the longer one.

true
false
true
true
true

Logical operators

Logical operators are used to test the truthiness of an expression consisting of one or more boolean values.

• Logical and returns true only if both members are true

• Logical or returns true if there is at least one member which is true

• Logical xor returns true if one member is true, but the other is not

• Logical not negates the truthiness of its member: changing true to false, and vice versa (it is the only logical operator that takes just one operand)

logicalOperators.nim

link:{source-dir}/logicalOperators.nim[role=include]

T and T: true
T and F: false
F and F: false
---
T or T: true
T or F: true
F or F: false
---
T xor T: false
T xor F: true
F xor F: false
---
not T: false
not F: true

Relational and logical operators can be combined together to form more complex expressions.

For example: (5 < 7) and (11 + 9 == 32 - 2*6) will become true and (20 == 20), which becomes true and true, and in the end this will give the final result of true.

Recap

This was the longest chapter in this tutorial and we covered a lot of ground. Take your time to go through each data type and experiment with what you can do with each of them.

Types might seem like a restriction at first, but they allow the Nim compiler to both make your code faster, and make sure you’re not doing something wrong by accident — this is especially beneficial in large code bases.

Now you know the basic data types and several operations on them, which should be enough to do some simple calculations in Nim. Test your knowledge by doing the following exercises.

Exercises

1. Create an immutable variable containing your age (in years). Print your age in days. (1 year = 365 days)

2. Check if your age is divisible by 3. (Hint: use mod)

3. Create an immutable variable containing your height in centimeters. Print your height in inches. (1 in = 2.54 cm)

4. A pipe has a 3/8 inch diameter. Express the diameter in centimeters.

5. Create an immutable variable containing your first name, and another one containing your last name. Make a variable fullName by concatenating the previous two variables. Don’t forget to put a whitespace in-between. Print your full name.

6. Alice earns $400 every 15 days. Bob earns $3.14 per hour and works 8 hours a day, 7 days a week. After 30 days, has Alice earned more than Bob? (Hint: use relational operators)