CS1 Lesson 1 Tutorial

Abhiram Chivukula

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• Publié par: Fiwyong
• Nombre de lectures: 59
• Langue: English

Extrait

Computer Programming 1

Lesson 1: Operators

By Abhiram Chivukula

Key Terms:

Compiler/Compile-

When you compile a program, the compiler tests to see if there are

syntax errors or logical errors in the program. The program is not executed or built.

Naming Conventions-

The use of alphanumeric characters and the underscore character

to name pieces of data. Names must start with an alphanumeric character. Depending on

your compiler, you may be given the option to turn on case-sensitivity, in which case the

names of data pieces will differ with capitalization.

Foreword:

This tutorial will be taught primarily in Pascal, but the concepts can be applied anywhere.

The basic structure of a Pascal program is as follows:

Program

Write_the_name_of_your_program_here;

Begin

Code

;

End.

Firstly, I would like to point a few things out. There is a rule called Naming Conventions,

and it applies to the names that you give to your program data. Naming conventions says

that you can have all and only alphanumeric characters and underscore in the names of

your program, and the name must not start with a number. This is not just done for

aesthetics, it is done so that the program will actually

compile

.

Secondly, with a few exceptions, every line of code in Pascal will have a Semi-Colon at

the end of the line. This is to let the

compiler

know that the end of the set of instructions

on that line has come and its time to start a new set of instructions. As you can see, there

is no semi-colon after Begin, and there is a reason behind that. Theoretically, your

program is itself a set of instructions, thus signifying that there should be no semi-colon.

The practical reason there is no semi-colon after Begin is that it just won’t

compile.

Thirdly, I would like to point out that after the word End, there is a period. This is to

signify that it’s the end of the program.

We will be expanding on the basic structure as we get to later tutorials.

Operators

Pascal and almost all computer languages take advantage of operators. Operators are

basically symbols that cause an action between two pieces of data, and return the result.

Some examples of operators are as follows:

+

Addition operator-returns the sum of two or more pieces of data

-

Subtraction operator-returns the difference of two or more pieces of data

*

Multiplication operator-returns the product of two or more pieces of data

/

Division operator-returns the quotient of two or more pieces of data

(

or

)

groups two or more pieces of data for use in mathematical operations. Encloses

Boolean statements.

^

Pointer operator-See the lesson on pointers to learn the use of this operator

Examples:

1+2 returns 3

1+-2 returns -1 (note, some compilers do not like this type of notation and force you to

write 1+(-2)

1-2 returns -1

99-1 returns 98

1*2 returns 2

1*-77 returns -77 (note, some compilers do not like this type of notation and force you to

write 1*(-77)

1/2 returns .5

-1/2 returns -.5

Programming Skills:

Essential Commands:

Writeln()- writeln simply writes out text to the screen. If you put a mathematical

expression, it will write out the evaluated result. You can also add words together in

writeln. Writeln goes to the next line after writing the text.

Readln()- for now we will use this only to make the program wait for you to see the

output. In this scenario, it waits for the user to press enter, but is commonly used to read

in a line of data from the keyboard.

Write()- Write does the same thing as writeln except it does not go to the next line after

writing text. It will simply write at the next available space.

Read()-Read serves almost the same functionality as readln, except that read only reads in

one character of the input.

The following program will make use of the operators we have talked about so far. Copy

and paste it into your compiler and run the program.

Program Operators;

Begin

Writeln(‘Hello, this is my operator program’);

Writeln(1+2);

Writeln( (1-2)*3 );

Writeln(1*2);

Writeln(1/2);

Readln;

End.

Notice that when you run this program, everything prints out fine until ½. For .5, it writes

it in exponential notation. This can be fixed with a simple formatter. Replace writeln(1/2)

with writeln(1/2:0:X) where X is any integer you choose. It will return the answer

accurate to X decimal places.