The BASIC computer programming language has been popular for many years, and there have been dozens of ‘dialects’ of the language. It’s considered a high-level language and is typically interpreted (rather than compiled). For this problem, write an interpreter for a restricted dialect of BASIC. Here is a description of the language.
Each input line contains one statement. Each statement begins with a non-negative integer, which we will call its label. Following the label is a single space and one of the following commands (with explanations following):
LET X = <ARITHMETIC_STATEMENT>
Assign the result of the arithmetic statement to variable
X.
IF <CONDITION> THEN GOTO L
If the boolean given is true, then go to the statement
labeled L, where L is a valid label. (If
the condition is not true, continue execution to the
statement with the next lowest label.)
PRINT <PRINT_STATEMENT>
Produce output, without an appended newline.
PRINTLN <PRINT_STATEMENT>
Produce output, with an appended newline.
Here are details on types, variables, and the terms <ARITHMETIC_STATEMENT>, <CONDITION>, and <PRINT_STATEMENT> used above.
All numeric values (in the input and for the variable representation) are signed 32-bit integers.
All variables are single uppercase characters (A through Z). They are all global in scope, and are all initialized to zero before program execution begins.
<ARITHMETIC_STATEMENT> is one of the following: X, X + Y, X - Y, X * Y, or X / Y. Here, X and Y each indicate either a variable or an integer.
<CONDITION> is one of the following: X = Y, X > Y, X < Y, X <> Y, X <= Y, or X >= Y. Again, X and Y each indicate either a variable or an integer. Here, <> indicates inequality.
<PRINT_STATEMENT> is either a variable name or a literal string delimited by double quotes. Inside the quotes, the string contains only alphanumeric characters (a-z, A-Z, 0-9) and spaces.
In the signed 32-bit arithmetic, the usual rules of truncation towards zero (for division) and overflow (for addition and multiplication) and underflow (for subtraction) apply. The following examples illustrate these conditions:
5 / 2 = 2 65536 * 32768 = -2147483648 -1 / 2 = 0 -65536 * 32768 = -2147483648 2147483647 + 1 = -2147483648 -2147483648 * 2 = 0 -2147483648 - 1 = 2147483647 2147483647 * 2 = -2
Further, division by zero will not occur.
Program execution begins with the statement having the smallest label, and proceeds with the statement having the next smallest label. (Unless a GOTO executes, in which case execution proceeds at the designated label.) The program halts after it has completed the statement with the largest label (which is guaranteed not to contain a GOTO).
Input consists of a single program. Each line contains a single valid statement. Each pair of adjacent tokens in the input is separated by a single space. Integers in the input will all be in the range $-2^{31}$ to $2^{31}-1$. Input ends at end of file.
Give the output (PRINT and PRINTLN statements) of the input program when it is executed.
Sample Input 1 | Sample Output 1 |
---|---|
10 LET A = 1 20 PRINT "HELLO THERE " 30 PRINTLN A 40 LET A = A + 1 50 IF A <= 5 THEN GOTO 20 60 PRINTLN "DONE" |
HELLO THERE 1 HELLO THERE 2 HELLO THERE 3 HELLO THERE 4 HELLO THERE 5 DONE |
Sample Input 2 | Sample Output 2 |
---|---|
40 PRINT P 180 PRINTLN "DONE" 130 PRINTLN " IS PRIME" 60 LET X = D * D 80 LET R = P / D 100 LET R = P - R 20 LET D = 1 140 IF 1 = 1 THEN GOTO 180 30 LET P = 111 150 PRINTLN " IS NOT PRIME" 170 PRINTLN " IS A DIVISOR" 50 LET D = D + 1 70 IF P < X THEN GOTO 130 120 IF 1 = 1 THEN GOTO 50 90 LET R = R * D 110 IF R = 0 THEN GOTO 150 10 PRINTLN "PRIME TESTER" 160 PRINT D |
PRIME TESTER 111 IS NOT PRIME 3 IS A DIVISOR DONE |