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After it is all typed in check it over for errors. Save your program and exit. If you are using DOS version, Press F2 key to save the program. Give it an appropriate name such as B:PROGRAM1.PAS (assuming your disk in B: drive). Now that you learned how to get into Turbo Pascal, write a program and save it, it is time to learn how to retrieve a file you saved. Just for practice, get out of Turbo Pascal: A ) Press F10 key B ) Choose File C ) Choose Exit Now get back into Turbo Pascal and open the file you just saved. Turbo Pascal brings up the program you saved earlier. A program is a set of instructions for a computer to carry out. Now we need to tell the computer to carry out these instructions; choose main menu by pressing F10, then choose Run. If you typed in everything correctly, a new screen will appear asking you enter the first number. If there are errors in your program, you will receive appropriate messages. Fix these bugs and Run it again. If you typed in everything correctly, it will ask you for the first number. Give it a whole number. It will now prompt you for the second number. Give it another whole number. There you have it, the program gave you the sum of these two numbers. Program run: Enter the first number to add 125 Enter the second number to add 5123 The total for these two numbers is: 5248
Let's talk about this program. A Pascal program begins with a reserved word PROGRAM and then a program name of your choice. Input and output given in parentheses tell Pascal that we are going to be using keyboard for input and monitor for output. In other words, you are going to type in the numbers using the keyboard, and the result will be displayed on the monitor. Next there is a VAR section. This is where you tell Pascal the names of the variables you would be using. A variable is a name of a memory location where the number you type in would be stored. (If you didn't follow that, please read the appendix 3A at the end of Chapter 3). In this program three variables are used, firstNumber, secondNumber, and Sum. All these variables belong to the same TYPE called integer (whole number). We just told Pascal we would be using only whole numbers, not fractions. The next section is enclosed in the BEGIN END pair. Thissection should be self explanatory. These are the instructionsneeded to read two numbers, total them and display the sumon the screen. EXPLANATION OF PASCAL WORDS OR SYMBOLS USED Since it is our first program, we have used a lot of new Pascal words and symbols. We will look at them very briefly here and will deal with them again at later chapters. PROGRAM This is a reserved word to be used at the beginning of a program. You cannot use this word in any other way within a Pascal Program. () Among other things, parentheses are used to pass arguments to a procedure. For example, WRITELN is a procedure; what you want to print on the screen is the argument, and it is enclosed in the parentheses. Another example..Writeln ('Good Day'); here 'Good Day' is the argument. ; A semicolon is used separate two pascal statements. VAR This is another reserved word to be used to declare the variables you would be using in a program or procedure. Variable declarations are explained in Appendix 2A. : A colon is used to indicate types of variables declared. BEGIN Begin and End pairs are used to enclose END The End statements between them. These statements are then considered to be a unit or a block. You can use as many of these as you wish, as long as they are paired. You can have a Begin/End pair inside another Begin/End pair (nested). := This is an assignment operator.Whatever is on the right of this symbol is assigned to the variable on the left of this symbol. Temp := 78 will assign 78 to Temp. write This is a procedure. You can use this to write results on the screen or into a file. writeln Same as write, except, writeln will add a line feed and a carriage return. In other words, if you use writeln, after writing a line the cursor will go to the beginning of the next line. Whereas the write statement keeps the cursor at the end of the current line. read read procedure is used to receive input from the keyboard or from a file. readln When using a keyboard, both read and readln work the same unless you give special compiler directives. When using a file, readln will read the current variable and skip the rest until the end of the line marker. More about read and readln: Read and Readln procedures allow the user to input data into the program through a file or a keyboard. The main difference between these is the position of the marker after execution of the statement. (When using the keyboard read and readln works exactly the same unless special compiler directives are given). The following examples assume that the input is from a data file. Example: var Year, Month, Day : integer; -------------------------------------------- position commentReadln(Year); 1982 █ marker on next line. Read(Year); 1982█ marker on same line. Readln(Year, Month, Day); 1989 2 13 █ marker on next line. Write and Writeln procedures also work similarly. Write procedure does not insert a carriage return and line-feed after execution, while writeln does. Here are some examples of how the combination of read, readln, write and writeln procedures work: Readln(Year); 1982 You entered 1982 Writeln('You entered ',Year); █ Readln(Year); 1982 You entered 1982█ Write('You entered ',Year); Write('Do '); Write('you '); Do you understand? Writeln('understand?'); █ When printing numbers, you can specify the number of spaces they should occupy. If the number is longer than spaces specified, then Pascal takes the necessary spaces. If the number is shorter then it is padded with spaces on the left. With real numbers, the number of decimal spaces that should appear on the output can be specified. Remaining decimals are rounded. Writeln (result:8:2); specifies that a total of 8 spaces will be allowed for the number including the decimal point. The whole numbers will be right justified and the fractional part will be aligned (left justified) with the decimal point. Writeln (result:1:2) will indicate to allocate two decimal places, but to left justify the whole number. Even though only one space is allocated for the whole number, Pascal would take required number of spaces to fit the whole number. But Pascal would not take any more spaces for decimal places than those allocated. Example: Given the following variables: var Age : integer; Weight : real; B : Char; Readln (Age,Weight,B); 40 130.5 a Writeln (Age:8); ^^^^^^40 (spaces are indicated with^) Eight spaces are allocated to write the value of age. Since age only requires 2 positions six spaces are added to the left. In another words age (40) is printed right justified! Writeln (Weight:10:2); ^^^^130.50 Writeln (Age:1); 40 Total of ten spaces are allocated to write the value of weight, two of which will be used for decimals, one will be used for the decimal point. So we have 7 spaces left to write the whole number portion of weight (130), which is printed right justified. However, in the next writeln statement, age is allocated one space. Since 40 cannot be written in one spaces, pascal takes the additional space necessary. This is a way to left justify a number. Writeln ('Age is: ',Age:4); Age is: ^^40 Writeln ('Statement is ',B); Statement is a Writeln (Weight:1:2); 130.50 Writeln ('Age ':6,Age:1); ^^Age 40 Everything inside the single quotes are considered to be character (string) literals. Everything inside the quotes will be printed exactly. If there are some characters without any quotes enclosing them they would be considered to be a variable identifier. Whatever the value of that variable is, that would be printed. You can also print literals also in a specified number of spaces. See example ['Age ':6] Age will printed in six positions. Notice this includes a space within the quote. Therefore, there are four characters to print, remaining two positions will be filled with blanks. If any of the explanation above was difficult to follow, don't worry. We will talk about most of these later or they are covered in the appendix. TURBO PASCAL Pascal is a high level structured programming language developed by Nicklaus Wirth in the early seventies. Turbo Pascal has added many enhancements to the original Pascal language by Wirth. Turbo Pascal has gone through several versions, the most recent one at the time of this writing is version 6.0. Turbo Pascal package comes with a powerful editor which is similar to the Word-Star's non-document mode. The compiler will allow you to compile the program to a file on a disk or to RAM. If compiled to the RAM you can run the program without leaving the Turbo Pascal environment. While running the program Turbo Pascal shows you the line of the program if error occurred. STARTING TURBO PASCAL. Turbo Pascal is installed in a subdirectory called TP or PASCAL. You can find out where it is by asking for a directory from the root. If it is in the TP subdirectory do the following: CD\TP PRESS <ENTER> ( this changes default to TP) TURBO PRESS <ENTER> ( this loads the program )
At the top of the screen five menu options are given: Once in the editor you can start typing your program. When finished writing the program press ^KD (press K while holding down the control key). If you wish to save the program choose the File option and choose the Save option. It will show the default file name NONAME.PAS and ask you to give it another name. Review the section on HOW TO NAME A FILE in Chapter 1. Once saved in a file, you can load the program back in to memory by choosing the Load option form the File menu. Try all other menu options to see how they work. It is a good idea to become thoroughly familiar with all options before getting into heavy programming. To quit Turbo Pascal choose the Quit option from the File menu. The pull down menu under option FILE provides many powerful features. Load, Save and OS shell will be discussed here. If you already have a file created and want to edit it, just load it. Choose Load and then type in the file name you want to load. If you do not remember the complete file name, you can give wild card characters. Example lab?????.pas or lab?????.*. The asterisk here stands for 3 question marks. *.* stands for ????????.??? (also known as global or star-dot-star). The OS shell provides a way for you to temporarily go to the DOS and execute any DOS command you wish. Then you may return to where you left off by typing EXIT. This powerful feature allows you to examine, print or create files from DOS. WRITING YOUR SECOND PASCAL PROGRAM
1 ) Change default working directory to Turbo Pascal 2 ) Type TURBO and press <ENTER> 3 ) Using arrow key highlight Edit and press <ENTER> 4 ) Type the following program: PROGRAM 2-2
Program run: Turbo Pascal Version 6.0 Copyright (c) 1983,90 Borland International Enter your height in Inches: 65 Enter your weight in pounds: 125 Your height in centimeters is 165.10 Your weight in kilograms is 56.70 Type EXIT to return to Turbo Pascal... Microsoft(R) MS-DOS(R) Version 5.00 (C)Copyright Microsoft Corp 1981-1991. C:\TP> 5. Press ^KD (Press K while holding control key and press D). Instead, you can press F-10.
6 ) Press F (for file). Notice this has the same effect as using
the arrow key. Place a formatted disk in
7 ) Press R (to run the program) or use arrow key to highlight Run and
press <ENTER>. When this
8 ) While the program is running pressing F5 (Function Key 5) will zoom
window that is running the
9 ) If you wish to get a listing of the program, go to edit mode and press
^KP. Or you can print the saved
10 ) If the program did not run, you may have typed it wrong. The arrow keys
can be used to pilot the MORE ON TURBO PASCAL COMMANDS. Insert : When you first enter Turbo Pascal, it is in the insert mode. This means whatever you type between two words will be inserted there pushing the word on the right forward. You can get into typeover mode by pressing the Ins key (or Control V). Delete: Delete the character the cursor is on ---> ^G Delete one word to the right of the cursor ^T Delete the whole line--------------------> ^Y Block: Go to the beginning of the section you want to block and press ^KB, then go to the end and press ^KK. Now you can do a lot of things with this block. If you wish to move it, go to the location you want to move it to and press ^KV (or ^KC to copy). If you wish to write the block to a file press ^KW. To delete a block press ^KY. Merge a file : Suppose you have a subroutine saved in a file and want to merge it with a program you are currently writing, you can use ^KR. Then it will ask for the filename you want to read in. Turbo Pascal 5.0 provides you with a set of hot keys (Press just one key instead combination ^KD etc.). Here are some : F1 - HELP F2 - SAVE CURRENT PROGRAM F3 - LOAD A FILE F5 - MAKE THE WINDOW YOU ARE WORKING WITH LARGER - ZOOM F6 - SWITCHES TO ACTIVE WINDOW F10 - CALLS THE MAIN MENU You can also use the Alt- and a key combination. For example, Alt-E to get into the editor, Alt-R to run the program, Alt-F to get into the File option, etc. ASSIGNMENTS FOR CHAPTER 2
1 ) Modify Program 2-1 to add three numbers instead of two. Make
sure to modify the write statements {Sum these numbers} {print the results to the monitor} > 3 ) Write a program to convert Fahrenheit to Celsius. Use Program 2-2 as a guide. > 4 ) Add appropriate comments (see assignment #2 above, use it as a guide) to Program 2-2. Go to top of this chapter |