R as a Calculator
The simplest way to use R is to use it as if it were a calculator. For example, if we want to know what two times two is, you may type
> 2*2;
[1] 4
The notation [1] indicates that the result is the first element. This is useful later when we have many elements for one variable such as a vector. If you carefully compare this to the previous command, you will notice that we added a semicolon (;) here. However, the result remains the same since the semicolon is used as the separator for multiple commands. Sometimes, you may want to use builtin functions in your calculations. Here are some examples:
Natural logs
> log(10)
[1] 2.302585
Note that this is returning the "natural log" of 10, which uses the base "e," which is a constant with an approximate value of 2.71828.
Log using base 10
> log10(10)
[1] 1
Exponentiation
> exp(2)
[1] 7.389056
Square Root
> sqrt(4)
[1] 2
Absolute Value
> abs(4)
[1] 4
>
Type in the following commands and describe your observations.
> # case 1 : 1+2 > 2+2; 2*3; 2/5 > # case 2 > 8/22*(23) > # case 3: > 3*5 * 4 /2 
When you observe the results, remember the rules for the order of operations: "PEMDAS."
PEMDAS (From http://www.mathsisfun.com/operationorderpemdas.html) Order of OperationsDo things in Parentheses First. Examples:
Exponents (Powers, Roots) before Multiply, Divide, Add or Subtract.
Multiply or Divide before you Add or Subtract.
Otherwise just go left to right.
How Do I Remember It All ... ? PEMDAS !

The video below provides nice introduction to R, including a review of mathematical operations that can be performed using R as a calculator.
Getting Started With R (R Tutorial 1.1) MarinStatsLectures [Contents]