Decimal
An integer can be specified in decimal,
base 10

echo 10;
echo -1;
echo 0;
echo 1452;
Octal
We use octal when we need a readable format for bit string in
group of 3.
rw-r--r-- = 110100100 (binary) = 644 (octal)
READ (1) WRITE (1) EXEC (1) = binary 111 = octal 7
READ (1) WRITE (1) EXEC (0) = binary 110 = octal 6
READ (1) WRITE (0) EXEC (0) = binary 100 = octal 4
97 (decimal) = 141 (octal)
97 % 8 => reminder 1
12 % 8 => reminder 4
1 % 8 => reminder 1
1*8^2 + 4*8^1 + 1*8^0 = 64 + 32 + 1 = 97
Binary
To conver
binary to octal, convert first to decimal, then to octal.

echo 0b110100100;
echo bindec(110100100);
echo decoct(0b110100100);
echo 0644;
echo 0b1010111100;
Hexadecimal
Base 16 notation, identified by its
leading 0x.

echo 0x121;
echo 0xFF;
Float
Be aware that the float data type is
not always capable of representing numbers.

echo (0.1 + 0.7) * 10;
echo (int) ((0.1 + 0.7) * 10);