SIMSCRIPT II.5 Programming Language

1. SIMSCRIPT II.5 Basic Concepts
1.1 Introduction
A computer program is a list of instructions directing a computer to perform certain operations on
data. A programming language is used by a programmer to describe the data and the actions to be
performed. SIMSCRIPT II.5 is one such programming language. Here is a simple example of a
SIMSCRIPT II.5 program:
read X and Y
add X to Y
print 1 line with Y thus
The Sum is: *****
stop
This program consists of four SIMSCRIPT II.5 statements. The statements are instructions to:
1. Read the values of two variables called X and Y from input data
2. Add these variables together
3. Print the sum of the variables along with the explanatory message, The Sum is:, and
4. Stop.
The example illustrates the basic computer operations of input (reading data), computation (in this
case, addition), and output (printing results).
In program examples throughout this book, SIMSCRIPT words and commands will be printed in
lower case characters. Variable names, routine names, and other user-supplied terms will be printed
in upper case characters. Thus, in the above example, read, and, add, to, print, line,
with, thus, and stop are all SIMSCRIPT words. X, Y, and the phrase, The Sum is: are expressions
provided by the programmer. SIMSCRIPT words which appear in the text (apart from
those in program examples) will appear in bold characters. Again, variable names appear in upper
case characters. Finally, small segments of code are presented in the ‘courier’ font as shown
above.
Although SIMSCRIPT does support string variables, the rest of this chapter focuses on integers and
reals. See paragraph 2.19.
1.2 Variables
As shown in the above example, programs use identifying names to refer to values of program variables.
A variable is a data item that may take on different values as it is acted upon by operations.
A program statement such as:
add X to Y
1