More About Data Types

The Basic Types

These are the basic types in Pike:

• integer (written int in Pike)
• floating-point number (written float)
• string (written string)

They are basic in the sense that data items of these data types can’t contain other data items. When a data item of a basic type is stored in a variable, it is the data item itself that is stored, and not just a reference to it, as explained earlier.

The Data Type int

Integer values can be written in several ways:

• In decimal (that is, base 10) format, i e the normal way to write numbers, such as 78.

• In octal (that is, base 8) format, with a leading 0, such as 0116 (which is equal to 78 in decimal notation).

• In hexadecimal (that is, base 16) format, with a leading 0x, such as 0x4e (which is also equal to 78 in decimal notation).

• In binary (ones and zeroes) format, with aleading 0b, such as 0b1001110 (which again is equal to 78 in decimal notation).

• As a character literal within single quotes, which will give the Unicode code point for that character. For example, 'N' will give the code point for the character N (which is equal to 78).

You can use normal arithmetic operations, such as addition and multiplication, with integers, but you can also consider integers as sequences of bits and, apply bitwise operations on them.

For example, the integer value 247 is stored internally as the sequence of bits 11110111, and you could left-shift it three positions with the expression 247 << 3, giving the bit pattern 11110111000, which is equal to 1976.

Integers in Pike can be very large. For small integers (usually less than 2 billion or so), Pike will use the computer’s own, hardware-supported way of representing integers. For larger integers, Pike will use “bignums”. These are slower, but can be arbitrarily large. Just like the smaller integers, bignums are represented exactly, without any rounding errors.

As a programmer, you will usually not need to worry about the difference between bignums and smaller integers. There may however be some operations, for example certain methods in certain C modules, that cannot handle bignums but work with smaller integers.

Some operations that you can apply to integers:

• Check if it is an integer

  intp(*something*) returns 1 if the value something is an integer, otherwise 0. Example:

  if (intp(u))
    write("The integer is " + u + ".\n");
  else
    write("It is not an integer.\n");
  

• Get a random number

  random(*limit*) returns a random value which is greater or equal to 0 and less than the integer limit.

• Reverse the bits

  reverse(*integer-value*) returns an integer with the bits in the integer-value in reverse order.

The Data Type float

Real numbers, which are numbers that can have a fractional part, such as 18.34 and -1000.03, are represented in the computer as floating-point numbers. Floating-point numbers can be used to represent very large numbers, but with limited precision. The number of significant digits is the same, no matter the magnitude of the value.

You can write floating-point values in two ways, as usual with decimals, or in exponential form with an e:

3.1415926535
-123.0001
12.0
1e6 // 1 times 10 to the power of 6, i e one million
2.0e-6 // 2.0 times 10 to the power of -6, i e two one-millionths
-1.0e-2 // Minus one hundredth

Some operations that you can apply to floating-point numbers:

• Check if it is a floating-point number

  floatp(*something*) returns 1 if the value something is a floating-point number, otherwise 0.

• Round downwards

  floor(*float-value*) returns the largest integer that is less than or equal to float-value, but as a floating-point number. For example, floor(7.3) gives 7.0 (and not the integer 7). If you do want the integer value, you can use an explicit type conversion: (int)7.3 gives you the integer 7.

• Round upwards

  ceil(*float-value*) returns the smallest integer that is greater than or equal to float-value, as a floating-point number. For example, ceil(7.3) gives 8.0 (and not the integer 8).

The Data Type string

Strings are sequences of characters, and are written within double quotes (") in Pike:

"scorch"
"Hello world!"
"Woe to you, oh Earth and Sea"
""

The last one is the empty string. Special characters, such as the double quote character, need to be preceded by a backslash character (\):

• \" to get a double quote (") in the string
• \\ to get a backslash character (\)
• \n to get a newline character
• \t to get a tab character
• \r to get a carriage return
• \0 to get a NUL character, i e the character with character code 0

Here are some examples of strings:

"One line\nAnother line\nA third line"
"Strings are written within \" characters."

You can use Unicode code points instead of the characters themselves. If you write \d followed by a decimal (that is, normal base 10) number, it will be replaced by the character with that Unicode code point. The same goes for \x followed by a hexadecimal (base 16) number, and a single \ followed by an octal (that is, base 8) number. The \0 is actually an example of this. These four strings are identical:

"Hello world"
"Hello \d119orld"
"Hello \x77orld"
"Hello \167orld"
"\d78""2OH" // "N2OH"

If the character following your code point number is also a number, follow your code point with "", to tell Pike that this was the end of your code point, and the following “2” is its own character, not another digit of the code point.

Strings in Pike are what we call “shared”, which means that if two or more strings contain exactly the same characters, there will still be only one copy of it in memory.

Some operations that you can apply to strings:

• Check if it is a string

  stringp(*something*) returns 1 if the value something is a string, otherwise 0.

• Concatenation

  Strings can be concatenated with the + operator:

  string s1 = "Hello";
  string s2 = " ";
  string s3 = "world!";
  write(s1 + s2 + s3 + "\n");
  

• Concatenation of string literals

  String literals, who are strings within double quotes that are written in a program, can be concatenated by just putting them after each other:

  write("Hello"  " "  "world!" + "\n");
  

  (This is, incidentally, how the terminated numeric escapes above work under the hood.)

Pike has many powerful built-in operations for working with strings. Read more about those in the chapter about string handling.