stackmachine wk 4 workshop

Week 4-workshop/README.md

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+## Workshop 3 content
+
+Workshop content: http://web.archive.org/web/20210817060220/https://teaching.csse.uwa.edu.au/units/CITS2002/workshops/workshop4.php \
+`stackmachine.c` template: http://web.archive.org/web/20210817060343/https://teaching.csse.uwa.edu.au/units/CITS2002/workshops/stackmachine.c \
+`stackinstructions`: http://web.archive.org/web/20210817060255/https://teaching.csse.uwa.edu.au/units/CITS2002/workshops/stackinstructions

Week 4-workshop/stackinstructions.txt

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+push  7
+push  3
+push  2
+subtract
+multiply
+push  5
+push  1
+add
+add

Week 4-workshop/stackmachine.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+//  written by Chris.McDonald@uwa.edu.au
+//
+//  compile:  cc -std=c11 -Wall -Werror -o stackmachine stackmachine.c
+
+#define STACK_SIZE 1000
+
+int stackmachine(FILE *input)
+{
+    int         stack[STACK_SIZE];         // a large stack
+    int         SP = -1;             // stack is initially empty
+
+    char        line[100];
+
+//  READ FROM input UNTIL WE REACH THE END-OF-FILE
+    while(fgets(line, sizeof line, input) != NULL) {
+        char word1[50], word2[50];
+
+//  SPLIT THE LINE INTO UP TO TWO WORDS
+        int wcount = sscanf(line, "%s %s", word1, word2);
+
+        if(wcount == 2) {
+            if(strcmp(word1, "push") == 0) {
+//              perform actions for the "push" instruction
+//              using word2 (an integer value)
+                stack[++SP] = atoi(word2);
+            } else if(strcmp(word1, "pop") == 0) {
+                SP--;
+            }
+
+//          add other instructions here....
+        } else if(wcount == 1 && SP > 0) {
+            if(strcmp(word1, "add") == 0) {
+//              perform actions for the "add" instruction
+                stack[--SP] = stack[SP] + stack[SP-1];
+            } else if(strcmp(word1, "subtract") == 0) {
+                stack[--SP] = stack[SP-1] - stack[SP];
+            } else if(strcmp(word1, "multiply") == 0) {
+                stack[--SP] = stack[SP] * stack[SP-1];
+            }
+//          add other instructions here....
+        } else if (SP < 2) {
+            fprintf(stderr, "HALT: Pointer out of range\n");
+            exit(EXIT_FAILURE);
+        }
+        if (SP < 0 || SP >= STACK_SIZE) {
+            fprintf(stderr, "HALT: Pointer out of range\n");
+            exit(EXIT_FAILURE);
+        }
+        
+        printf("%d\n",stack[SP]);
+
+        if(wcount == 0) {
+            fprintf(stderr, "HALT: unrecognised line: %s\n", line);
+            exit(EXIT_FAILURE);
+        }
+    }
+
+//  RETURN THE FINAL RESULT (FROM THE TOP-OF-STACK)
+    return stack[SP--];
+}
+
+int main(int argc, char *argv[])
+{
+    int result;
+    argv[1] = "./stackinstructions.txt";
+//  CHECK THE NUMBER OF ARGUMENTS
+    if(argc > 1) {
+        FILE *fp        = fopen(argv[1], "r");
+
+//  ATTEMPT TO OPEN AND EVALUATE THE INSTRUCTIONS FROM A FILE
+        if(fp == NULL) {
+            fprintf(stderr, "HALT: cannot open '%s'\n", argv[1]);
+            exit(EXIT_FAILURE);
+        }
+        result = stackmachine(fp);
+        fclose(fp);                     // we opened it, so we close it
+    }
+
+//  OTHERWISE, EVALUATE THE INSTRUCTIONS FROM stdin (THE KEYBOARD)
+    else {
+        result = stackmachine(stdin);
+    }
+
+//  PRINT THE FINAL RESULT (FROM THE TOP-OF-STACK)
+    printf("result = %i\n", result);
+
+//  YOU CAN PROVIDE ANY (OR ALL!) OF THE FOLLOWING LINES (DOESN'T MATTER)
+    exit(EXIT_SUCCESS);
+    return EXIT_SUCCESS;
+    return 0;
+}