String Functions

Strings are sequences of characters. They are useful for storing data and also for accepting user input, whether it be from a terminal command line or a web form.

I find these particular string functions indispensable in my own web programming. I'm sure there are many other frequently-used string functions.

Action	C++	PHP	JavaScript
Split a string into an array of strings	–	explode	split
Compare strings	compare	strcmp	< or >
Find a character within a string	find	strchr	indexOf
Get length of string	size	strlen	length
Find a string within a string	strstr	strstr	indexOf
Convert a string to hexadecimal	std::hex	–	toString(16)
Get a substring	substr	substr	substring
Convert string to floating point	atof	floatval	parseFloat
Convert string to integer	atoi	intval	parseInt
Upper case first character	toupper	ucfirst	toUpperCase
Trim white space	–	trim	trim
Replace	replace	str_replace	replace
Regular expression replace	c	preg_replace	replace
Determine if string is a number	–	is_numeric	!isNan

There are also a few useful functions that relate to single characters only, but they are usually used in the context of string processing.

Action	C++	PHP	JavaScript
Get the ASCII value of a character	–	chr	fromCharCode
Determine if character is a digit	isdigit	ctype_digit	parseInt and slice
Determine if a character is upper case	isupper	ctype_upper	compare with toUpperCase

Decisions Using the Switch Statement

You can also make decisions using the switch statment. It looks like this:

switch (exponent) {
    case 0 :
        // do nothing
        break;
    case 1 :
        input = input * 10;
        break;
    case 2 :
        input = input * 100;
        break;
    case 3 :
        input = input * 1000;
        break;
    default :
        // do nothing
        break;
}

The above code implements simple exponentiation for languages that do not support it natively. Note that each case is an integer. The general rule is that the different cases must be types that can be converted to integer at compile time. The computer science term for such types is "enumerable." Integers, characters, and enumerations would be valid here. (An enumeration is just a way of giving names to different integers, like constant literals.) Characters are valid enumerable types because they can be considered a restricted set of integers. For example, the letter 'A' evaluates to the integer 65. See the ASCII character set for more information.

Decisions and Branching

We must have a way for the program to make a decision, and then execute different code based on the decision. If the number is less than 10, we do one thing, otherwise we do something else. If the object is a rectangle, we obtain the area by multiplying its width by its height; but if the object is a circle, we obtain its area by multiplying its diameter by π.

Indeed, I would venture a guess that the majority of the time, popular computer programs are making decisions. (This is less so for scientific programs that do extensive numerical computations.)

Foundational Programming Concepts

I teach three programming classes. There are several concepts that I must teach in all my classes because they are so foundational. Once you have mastered these concepts in any programming language, it is easy to transfer the knowledge to other languages.

• Decisions and Branching
• Loops
• Arrays
• Functions
• Strings
• Data

Boolean Logic

Boolean logic is a way of describing relationships between ideas that can have the truth values TRUE and FALSE. We describe these relationships in a diagram called a truth table:

x	y	x OR y	x AND y
False	False	False	False
False	True	True	False
True	False	True	False
True	True	True	True

Here is an example of boolean logic. Suppose we have a set of colored shapes. We might ask two kinds of questions. If we choose one of the colored shapes, we might ask: is it blue and a circle? If we choose a blue circle, it is blue and also a circle. If we choose a yellow circle, it is not blue and a circle, because it is yellow (not blue). If we choose a blue square, it is not blue and a circle, because it is a square (not a circle). So whatever shape we choose must satisfy both the requirements, that it be both blue and also a circle.