This program was an assignment for my Programming Languages course. The idea is to implement a simple pseudocode interpreter which has very basic functionality as well as a contiguous memory store. Here is how it works:
- You feed the program a CRLF separated list of valid syntax. In this case, the file “pseudocode.txt” which should be in the same directory as the program (no file picker implemented).
- The program reads, parses, and executes the given instructions
- Any errors that are found are reported, else the program runs until STOP instruction or EOF.
The instruction set is very limited. There are a total of about 18 operations which can have 2 operands. If something is contained in [brackets] then that is referring to one of the 1000 available memory locations ([0] to [999]). You will find the instruction format in the source code, but here is a better explanation:
Instruction format:
| Explanation: |
| Valid inputs: |
Instruction Operation List (sf):
| sf value: |
| +0 |
| +1 |
| +2 |
| +3 |
| +4 |
| +5 |
| +6 |
| +7 |
| +8 |
| +9 |
| -0 |
| -1 |
| -2 |
| -3 |
| -4 |
| -5 |
| -6 |
| -7 |
| -8 |
| -9 |
Here is a sample program with an explanation:
10 -0 10 0 7
20 +1 7 25 5
30 -8 0 0 5
40 +9 0 0 0
- Line #10 stores the value 10 at memloc[7].
- Line #20 adds the value at memloc[7] (which is 10) to 25 and stores the result at memloc[5]
- Line #30 prints the value stored at memloc[5] which is 35.
- Line #40 terminates the program
/*
* Bradley Carey - CS300 - Assignment 1-2 "pseudocode"
* Simple pseudocode interpreter - default input file is "pseudocode.txt"
*
* Error codes: -1 syntax error, -2 divide by zero, -3 line number not found, -4 exit immediately, -5 unknown error
*/
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <sstream>
#include <cmath>
using namespace std;
const int debug = 0;
struct instruction
{
/* instruction format:
## s f xxx yyy ddd
## = line number, s = sign, f = function, xxx = operand1,
yyy = operand2, ddd = destination */
int lineNumber; // #
char s; // s
int f; // f
int xxx; // xxx
int yyy; // yyy
int ddd; //ddd
};
struct pseudoarray
{
int start;
int end;
int size;
};
//finds location in container holding desired linenumber and returns it
int findLineNumber(vector<instruction> container, int numToFind)
{
for(unsigned int i=0; i < container.size(); i++)
{
if(container[i].lineNumber == numToFind)
return i;
}
return -3;
}
//simple cin get function
int getNumber()
{
cout << "Please enter a number: ";
int read;
cin >> read;
return read;
}
//parse instruction
instruction parseLine(string lineToParse)
{
instruction storeThis;
istringstream buffer(lineToParse);
int num, f, xxx, yyy, ddd;
char s;
buffer >> num >> s >> f >> xxx >> yyy >> ddd;
if(debug)
cout << "Parsed line #" << num << " s: " << s << " f: " << f
<< " xxx: " << xxx << " yyy: " << yyy << " ddd: " << ddd << endl;
storeThis.lineNumber = num;
storeThis.s = s;
storeThis.f = f;
storeThis.xxx = xxx;
storeThis.yyy = yyy;
storeThis.ddd = ddd;
return storeThis;
}
// print instruction details
void printInstruction(instruction toPrint)
{
cout << toPrint.lineNumber << " " << toPrint.s
<< toPrint.f << " " << toPrint.xxx << " "
<< toPrint.yyy << " " << toPrint.ddd << endl;
}
/* parse and execute instruction
* return line number to jump to or a negative error code
*/
int executeInstruction(instruction toExecute, int memory[])
{
if(toExecute.s == '+')
{
switch (toExecute.f)
{
case 0: // +0, Move xxx to ddd
if(debug)
cout << "\tExecute +0 [Move]" << endl;
memory[toExecute.ddd] = toExecute.xxx;
return 0;
case 1: // +1, [xxx] + yyy result @ ddd
if(debug)
cout << "\tExecute +1 [+]" << endl;
memory[toExecute.ddd] = (memory[toExecute.xxx] + toExecute.yyy);
return 0;
case 2: // +2, xxx * yyy result @ ddd
if(debug)
cout << "\tExecute +2 [*]" << endl;
memory[toExecute.ddd] = (toExecute.xxx * toExecute.yyy);
return 0;
case 3: // +3, xxx * xxx result @ ddd
if(debug)
cout << "\tExecute +3 [Square]" << endl;
memory[toExecute.ddd] = (toExecute.xxx * toExecute.xxx);
return 0;
case 4: // +4, if [xxx]=[yyy] then goto ddd
if(debug)
cout << "\tExecute +4 [=]" << endl;
if(memory[toExecute.xxx] == memory[toExecute.yyy])
return toExecute.ddd;
else
return 0;
case 5: // +5, if xxx >= yyy then goto ddd
if(debug)
cout << "\tExecute +5 [>=] goto " << toExecute.ddd << " if " << memory[toExecute.xxx] << " >= " << memory[toExecute.yyy] << endl;
if(memory[toExecute.xxx] >= memory[toExecute.yyy])
return toExecute.ddd;
else
return 0;
case 6: // +6,
if(debug)
cout << "\tExecute +6 [x(y)->z]" << endl;
memory[toExecute.ddd] = memory[toExecute.xxx + memory[toExecute.yyy]];
return 0;
case 7: // +7, increment xxx and test
if(debug) // [xxx]++; if [xxx] < [yyy] then go to ddd;
cout << "\tExecute +7 [Increment and test]" << endl;
toExecute.xxx++;
if (toExecute.xxx < toExecute.yyy)
return toExecute.ddd;
else
return 0;
case 8: // +8, store input @ ddd
if(debug)
cout << "\tExecute +8 [Read]" << endl;
memory[toExecute.ddd] = getNumber();
return 0;
case 9: // +9,
if(debug)
cout << "\tExecute +9 [Stop]" << endl;
return -4;
default: // syntax error
if(debug)
cout << "\tExecute +? (???)" << endl;
return -1;
} // end + switch
} else {
switch (toExecute.f)
{
case 0: // -0,
if(debug)
cout << "\tExecute -0 (Move literal)" << endl;
memory[toExecute.ddd] = toExecute.xxx;
return 0;
case 1: // -1, xxx - yyy, result in ddd;
if(debug)
cout << "\tExecute -1 (-)" << endl;
memory[toExecute.ddd] = (toExecute.xxx - toExecute.yyy);
return 0;
case 2: //-2, xxx / yyy, result in ddd
if(debug)
cout << "\tExecute -2 (/)" << endl;
if(toExecute.yyy == 0)
return -2;
memory[toExecute.ddd] = (toExecute.xxx / toExecute.yyy);
return 0;
case 3: //-3, sqrt(xxx), result in ddd
if(debug)
cout << "\tExecute -3 (Square Root)" << endl;
memory[toExecute.ddd] = sqrt((double)toExecute.xxx);
return 0;
case 4: // -4, if xxx != yyy goto ddd
if(debug)
cout << "\tExecute -4 (!=)" << endl;
if(memory[toExecute.xxx] != memory[toExecute.yyy])
return toExecute.ddd;
else
return 0;
case 5: // -5, if [xxx] < yyy goto ddd
if(debug)
cout << "\tExecute -5 (<)" << endl;
if(memory[toExecute.xxx] < toExecute.yyy)
return toExecute.ddd;
else
return 0;
case 6: // -6, move contents of [xxx] to (memLoc[yyy]+contentsOf[ddd])
if(debug) // xxx yyy ddd
cout << "\tExecute -6 (x->y(z))" << endl;
memory[toExecute.xxx] = memory[toExecute.yyy + memory[toExecute.ddd]];
return 0;
case 7:
if(debug)
cout << "\tExecute -7 (Decrement and test)" << endl;
return 0;
case 8: // -8, print xxx literal or what is @ location ddd
if(debug)
cout << "\tExecute -8 (Print)" << endl;
cout << "Value at [" << toExecute.ddd << "]: " << memory[toExecute.ddd] << endl;
return 0;
case 9:
if(debug)
cout << "Execute -9 (Program Comment)" << endl;
return 0;
default: // syntax error
if(debug)
cout << "Execute -? (???)" << endl;
return -1;
}
return -5; // unknown error
}
}
int main()
{
int programMemory[1000] = {0};
ifstream openFile;
vector <instruction> codeContainer;
string currentLine;
// open, parse, and store source file in vector<instruction> codeContainer
openFile.open("pseudocode.txt");
if(!openFile)
return 0;
while (getline(openFile,currentLine))
codeContainer.push_back(parseLine(currentLine));
openFile.close();
//print parsed pseudocode.txt
if(debug)
{
cout << "Parsed " << codeContainer.size() << " total lines of code successfully." << endl << "Source code";
for(unsigned int i=0; i < codeContainer.size(); i++)
printInstruction(codeContainer[i]);
}
//execute instructions and handle error codes
for(unsigned int j=0; j < codeContainer.size(); j++)
{
instruction toExecute = codeContainer[j];
if(debug)
{
cout << "\tExecuting line ";
printInstruction(toExecute);
}
int result = executeInstruction(toExecute, programMemory); //returns 0 if successful, else returns line # to jump execution to
if(result)
{
if(result == -4) // exit immediately via +9
goto exit;
if(result == -1) // syntax error
{
cout << "=== Fatal error -> Syntax error" << endl;
goto exit;
}
if(result == -2) // divide by zero error
{
cout << "=== Fatal error on line #" << toExecute.lineNumber << " -> divide by zero" << endl;
goto exit;
}
if(result >= 1) // if >=, then jump to program line # result
{
int lineNumberReturn = findLineNumber(codeContainer, result); // returns 99999 if invalid line #
if(lineNumberReturn == -3) // line # not found
{
cout << "=== Fatal error on line #" << toExecute.lineNumber << " -> Invalid value for ddd ["
<< toExecute.ddd << "] ===" << endl;
goto exit;
}
else
j = lineNumberReturn-1;
}
}
}
exit:
cout << "Press enter to exit..." << endl;
return 0;
}