Defining strings in your programs three different ways: with single
quotes, with double quotes, and as a here document.
Escaping: what it is and what characters need to be escaped in each
kind of string.
Validating a string by checking its length, removing leading and
trailing whitespace from it, or comparing it to another string.
Formatting a string with printf( ).
Manipulating the case of a string with strtolower(
), strtoupper( ), or ucwords(
).
Selecting part of a string with substr( ).
Changing part of a string with str_replace( ).
Defining numbers in your programs.
Doing math with numbers.
Storing values in variables.
Naming variables appropriately.
Using combined operators with variables.
Using increment and decrement operators with variables.
Interpolating variables in strings.
