Floating-point calculations. Then we look up the value of the middle between MIN and MAX, index number 5, equal to 48. If A is not equal to one of these values, we will get an error. BASIC arrays can be also multi-dimensional (have more than one INDEX), for example to store ten points each holding 2 coordinates (X and Y) we can declare an array as DIM PT(10,2) and reference i-th point X coordinate as PT(i,1) and Y as PT(i,2). For example, to make a rectangle area dark blue, we can make each of its odd rows black Error codes can be determined by calling For example, when sorting numbers in the ascending order (as in the example above) after pass one the largest number is stored in A(8). Second, we added a special value R2, which will hold the square of R, so that we don't calculate this value over and over as part of calculating Y on LINE 70. Sometimes in your program you want to include information which will be used every time the program runs. If A is greater than zero, repeat step #1, using new value of A, but write the next 1 or 0 to the left of the bits already written. Version #1 uses GOTO, version #2 calls GOSUB. And I am using Applesoft BASIC as a tool to accomplish this goal. We get the different result because this time we are adding only odd numbers: 1,3,5,7 and 9. For this we use (optional) LET keyword. To store a number, it converts it into special format having only 1s and 0s. In the loop we will increment values of both variables and check the result: As we see, even though variables F and D get changed in LINE 60, the FOR loop still uses their values set at the start of the loop. Stop. How many different colors we can get using a 50/50 mix of 2 colors? This is not the only way to convert binary to decimal: we can do this by walking the entered string from LEFT to RIGHT. The remaining candidate solutions are numbers at indexes 3, 4 and 5. The method when we need to check all elements is called. INPUT command. When comparing two strings, we take first symbols in both strings and compare their ASCII codes; the one with a smaller ASCII code is considered a "smaller" string; in case the first symbols of both strings are the same, we look at the second symbol in each string, and so on, until we find a mismatch. In hi-res graphics you can plot a line between 2 points with HPLOT X,Y to X2,Y2 command. We compare values of variables A and B. Modern computer screens support thousands of colors. We then ask the user to enter 5 numbers and put them into array elements, one by one. Until now we used variables to store individual values. Applesoft BASIC Quick Reference. We will set them initially to 10 and 1. The following program prints numbers 0 to 20 in decimal and hexadecimal format: The procedure of converting a decimal number to hex format is moved to a subroutine starting at LINE 200. Files may be deleted from the VFS. LINE 10 clears the screen (with HOME command) and then sets text mode (with TEXT command). String and type conversion functions. are parsed with distinct cases for each statement type. LINE 90 is the shortest one. This way you will learn more about Another computer number format: hexadecimal numbers, Detecting which key was pressed: ASCII codes, Combining it all together: Snake game prototype, Initializing array with arbitrary number of with DATA elements. However, we are doing a lot of repeating calculations. in a program showing a calendar, you want to store the names of all 12 months, and also the number of days typically present What happens if one of the elements holds a string which cannot be converted to a number? Calling subroutines with GOSUB. One interesting use of FOR loops in BASIC is to create a delay. Which in turn means less points and then this new value is compared to 10. How this variable changes if we want to find the value of square root with a higher precision (change the 0.00001 on LINE 330 to 0.000001)? What is the most likely outcome? The Apple II series (trademarked with square brackets as "Apple ][" and rendered on later models as "Apple //") is a set of home computers, one of the first highly successful mass-produced microcomputer products, designed primarily by Steve Wozniak, manufactured by Apple Computer (now Apple Inc.) and introduced in 1977 with the original Apple II. We also can fix this issue by introducing a temporary variable (called T in our example below) on line 25, which is then used in both IF commands on line 30 and 40: To finish this section on IF-THEN-ELSE construct it's worth pointing out to another AppleSoft BASIC construct: "ON..GOTO", which directs program to different line numbers depending on the value (1,2,3..) of the evaluated variable: In our example above we ask the user to enter value for A. Notice LINE 35 with GOTO 70 command which tells the program to skip the rest of the current cycle. CHR$ (CODE) returns the string with a single character with supplied ASCII code. The important decision about how many points to use with this method depends on the size of the circle itself. We create an array, write to a randomly selected element and then print it out, and finally use CLEAR to destroy the array (and all the other variables in the program). Is there a way to make graphics interesting with only 8 colors? API available in Web browsers is not standardized and is poorly defined; This program is rather involved, so some explanation is due. Convert hex string to binary string by calling two subroutines in a row: the first one converts hex to decimal, and second one converts the decimal we got to a binary. ): We can exit the FOR loop if necessary even before the loop variable reaches its final value by calling GOTO and redirecting the program somewhere outside the loop. In GR and HGR mixed sub-modes have four TEXT-mode lines on the bottom of the screen. binary numbers and about BASIC. In the previous example we included FN ROUND() function to round any argument to the nearest integer. In this lesson we will look how a simple sorting can be done in BASIC using arrays. It's worth noting that A in this case must be 1,2 or 3 (since we list only 3 options after GOTO command). which are used as arguments for the library calls. The following program prints 10 rows of numbers, row by row, with about one-second delay. FOR loop started on LINE 80 has corresponding NEXT command on line 110. To switch between them Here are the string functions and type conversion functions which convert string to numbers and vice versa: Let's take a closer look at this program. The binary search part of the program is a subroutine at LINES 300..360. First, we ask the user to enter desired radius, between 1 and 96. The following program takes input string from user and outputs the same string in the center of the screen. So how computer stores the rest of the web page, it is not available. Here is the modified program: Let's try more strings, this time with digits and lowercase letters: As you can see, the string starting with a digit ("2015") is on top of the list, followed by strings starting with uppercase letters, and then followed by all lowercase words. On LINE 40 we use ON..GOTO construct to direct the program to line 100,200 or 300 depending on value of A. Two variables, L (low) and H (high) control the current interval search limits. from 32-126 (printable ASCII). separator, Write down a symbol representing this number in hex form: for numbers 0-9 write digits zero to nine, for numbers ten to fifteen use letters (A=10,B=11,C=12,D=13,E=14,F=15). It would be very inconvenient to individually declare 100 variables and coming up with unique name for each. The following program shows all 21 colors which are either solid or a 50/50 mix of two solids we have. For example, MID ("STRING", 2, 3) returns string "TRI". In low-res graphics you can plot horizontal or vertical lines using HLIN and VLIN commands. data-declaration Most examples in this tutorial don't depend specifically on which text mode they run in; however in cases where it matters you should not forget to set the proper mode. You have to call them with "FN" and space preceding the function name. There is a number of opinions about BASIC as first programming language to teach. Some of them can be, In this section we will look at the BASIC program for finding the greatest common divisor (or GCD) of two natural numbers. Possible values of B are zero to fifteen. We call their indexes MIN=1 and MAX=9. It quickly became a popular educational tool for computer science due to its ease of use. But this difference is very important: in version #1 we loop through all numbers in one subroutine; in version #2 we call the same subroutine we are already in - and will be using in it a new value of A, until A is greater than zero. If A is even, write 0. Then we print the result with no more than 4 digits after decimal point (our guaranteed precision) on LINE 60. In the following example we add only values of N greater than 5. LINE 20 starts FOR loop using variable C (color). with a standard recursive descent parser. The token types (treated as terminals) are Modify the above program to sort numbers in the descending order (large to small). Then assign the result of the division to A. CHR$(65) returns "A". The page attempts to emulate an Apple II keyboard. with the Left Alt and Right Alt keys respectively if possible, Onboard Applesoft BASIC. Make the program above (using DATA commands) draw a different letter or a symbol. For this, you should use official manuals and references. Along with our distinct solid 6 colors, it makes a total of 21. consumed by a recursive descent parser which outputs a JavaScript We keep dividing the interval until it gets smaller than 0.00001 (LINE 340), when we know the square root of V with precision of no less than 0.00001. The length of circumference is 2*PI*R, so to make the circle look smooth we adjust the number of points proportionally. you should be careful with declaring variables with similar names. What if we want to store a 100 values? So in order to print something starting on third line from top of the screen, at the leftmost position, you set cursor position with "VTAB 3 : HTAB 1". Lines 80..88 plot eight points using only one given pair of (X,Y) from the first octave (first 1/8-th of the whole circle). Then we will write a program which converts a binary to decimal. please write. HGR2 resolution is 280x192 pixels. — take a peek at the code if you want the gruesome details. We will get down to the details of this program. One way to deal with this is to mix colors; this is similar to mixing two or more paints to create a new color. Modern languages typically use the value of the current time, in seconds or milliseconds as a way to get a random seed. with POKE 32,n ... POKE 37,n. BASIC building blocks: IF, GOTO, FOR..TO commands and BASIC variables, IF command and boolean operators AND, OR, NOT, AppleSoft BASIC missing IF-THEN-ELSE construct, Using trigonometric functions to draw a circle, More examples with trigonometric functions. For this we use the IF command which is check for a condition (A < B). to calculate and draw, so it can be done comparatively quicker. This approach makes it easy to output the final X: we simply call PRINT X. The original version was designed by John G. Kemeny and Thomas E. Kurtz and released at Dartmouth College in 1964. Note that the keyboard Think for example of your cell phone contacts: when you open the list of contacts they appear on screen ordered alphabetically, from A to Z. Variable names may contain numbers, but must begin with English letter. Let's check how these colors and pixels actually look: If you are serious about learning programming, you know that computers save all information as ones and zeros. In this last program, we split the program into several blocks: LINES 10..100 are the main program, LINES 300..350 is another block called a subroutine, and LINES 400..450 is another subroutine. The numbers you get from RND(1) function aren't truly random (this is why they are called pseudo-random! in every month. In case condition is not met, BASIC goes automatically to the next line #40. If you think I missed something that must be explained to a beginner programmer, I also need to decide what should be the size of array (CAP variable) to keep all prime numbers between 1 and N, to avoid overflowing of the array. So, how do we get a different seed value each time when program starts? We know that we need to look only at elements with indexes between 1 and 5 inclusive to find the best match. BASIC emerged in 1964 on the Dartmouth College Time Sharing System. The last number which gets added is 9.5 (why? It contains the END command telling BASIC that it should stop the program. For N=1000, we make prime array sized at 340. For this, you can create another array and move all elements into it one by one, checking for duplicate values (is there a better way to do this, without the second array?). This way the program is much smaller and also easier to understand: In this implementation, we determine the length of the entered string (LINE 120). In this implementation I am playing a trick: even though X denotes a binary number, I internally store it as decimal. This is not necessary, but is done so that we could see values of A and B on each iteration (step) of the algorithm. ): computer uses an algorithm to generate them, and when program restarts, the same algorithm produces the same sequence of values.