[Diegorkable]

Hey guys,

I need help with an algorithm im trying to develope, maybe you'll come up with a good one. Try to think and tell me...

how can I analyze a mathematic 'question' that is written in string and make it an answer in integer?

For example, I have:

PHP Code:

public mathExampleQuestion()
{
        new question[] = "3 + 3 x 3 / 3 + 3"
        
        // How do I loop through the string cells and analyze the answer converted to integer? (decimal value)
} 


I'll tell you why its hard? its hard cuz we must follow the math rules, it means '*' and '/' first, only then you can '+' or '-' them.

Got any ideas?

EDIT: By the way, I actually thought of an algorithm but isnt sure if its the best one. Loop through the string cells and solve all the '*' and '/' expressions, then when you get to an answer of the first experssion for example, you copy the answer into a new string, then the next sign must be '+' or '-' cuz its looping till it find '*' or '/' and solves the expressions with it, then stops to solve when it doesnt find it (the '*' or '/'), then after I found the first expression, I add the next expression, of for example '+' or '-'. so for conclusion, solve all the expression with '*' or '/' then post the answers of them into a new string with the signs between, I'll show a code example:

PHP Code:

public example()
{
    new question[] = "3 + 3 x 3 / 3 + 3"
    
    // Loop through the string and solve all the expressions with '*' or '/'
    // after make that a new string with the signs of '+' or '-' between
    // After the operation the new string would look like this:
    
    new analyzedQuestion[] = "3 + 3 + 3"
    
    // Then I can easily loop through this string and solve it by checking the sign
    // if its - or +
} 


[Sylwester]

Solving parts of equation and going back to string makes no sense. You just need to use a stack to temporarily store parts that can not be solved at the moment.

Simple example (no error checking, only positive integers, no brackets):

PHP Code:

public mathExampleQuestion(){
    new question[] = "3 + 3 x 3 / 3 + 3"
    
    new stack[6], top
    for(new i; i<sizeof question; i++){
        switch(question[i]){
            case '0'..'9': stack[top] = stack[top]*10+question[i]-'0'
            case '+','-','/','*','x':{
                while(top > 0 && (stack[top-1] == '*' || stack[top-1] == 'x' || stack[top-1] == '/' || question[i] == '+' || question[i] == '-')){
                    switch(stack[top-1]){
                        case '+': stack[top-2] += stack[top]
                        case '-': stack[top-2] -= stack[top]
                        case '/': stack[top-2] /= stack[top]
                        case '*','x': stack[top-2] *= stack[top]
                    }
                    top -= 2                    
                }                
                stack[++top] = question[i]            
                stack[++top] = 0                
            }
        }
    }
    while(top>0){
        switch(stack[top-1]){
            case '+': stack[top-2] += stack[top]
            case '-': stack[top-2] -= stack[top]
            case '/': stack[top-2] /= stack[top]
            case '*','x': stack[top-2] *= stack[top]
        }
        top -= 2
    }       
    client_print(0, print_chat, "%s = %d", question, stack[top])
} 


[Diegorkable]

Damn I like your logic! Took me like 10 minutes to understand it, thought first that the while was in the for so it confused be. Btw a question, I think you dont need to use in the "while (top>0) the case of '*', 'x', '/', cuz in the for all those signs are cancelled and only the '+' or '-' are left, so the array would look like that after analyzing:

stack[] = { 3, '+', 3, '+', 3 }

EDIT: By the way, just so you know, what I suggested is just the same as you. Solving the 'hard to solve' parts, then copying it to a new string. The same I did, I can post the code I created if you want.

[Sylwester]

You didn't understand it. It's not the same as your idea. You said that you want to solve '/' and '*' first, but that's not what I'm doing (see in my algorithm stack will store max 2 operators and 3 values at any time, so something like "3 + 3 + 3 + 3 + 3 x 3 / 3 + 3" wouldn't fit).

My idea goes like this:
When finished reading value from string check last operator (max 2 times at once).
If last operator is * or / then solve it.
If last operator is + or - then solve it if next operator has the same priority.
This way there will be no need to keep more than 5 elements on stack.

"while" loop is needed instead of "if" to avoid problem with example: 3 + 3 * 3 + 3 * 3
On stack: 3 + 3 * 3, next operator is +, so solve 3 * 3, but if there was no loop that also solves 3 + 9 then it would end with stack 3 + 9 + 3 * 3 (index out of bounds) instead of 12 + 3 * 3.

[Diegorkable]

I actually did understand it, and my idea was same to yours cuz, once again, i suggested calculating the problematic places with the * and / and writing it as a new string (in your case its the stack with { value, operator, value ... }).

By the way in that case: 3 + 3 * 3 + 3 * 3

The 'for' will make it: { 3, '+', 9, '+', 3, '*', 3 }, so yeah i understand why its needed. ( the case of '*' or '/' in the while )

[Diegorkable]

I tried to let it solve "2 - 6 x 4 x 3" and the answer is -70, and it didnt say it was -70, can you find any bug about that type of question?

EDIT: There was also "0 x 6 + 3", and the answer was 7 for some reason! why is that?
Another EDIT: Another case was "9 x 9 - 1", and it said the answer is 88... :S whats wrong, most of the questions it does good but sometimes it fucks up

[Sylwester]

I get these results:
2 - 6 x 4 x 3 = -70
0 x 6 + 3 = 3
9 x 9 - 1 = 80

You probably edited it and broke something.

[Diegorkable]

Yep that might be it, thanks still.

[Diegorkable]

Look there's something wierd...

I gave it a question, "9 x 2 x 4"
I have a global variable called 'Answer' and I store inside the question's Answer.
Also I scripted a command to see the result, and the answer, for some reason, for this question , was 430...

PHP Code:

new Answer, aQuestion[] = "9 x 2 x 4"

public plugin_init() {
    register_plugin(PLUGIN, VERSION, AUTHOR)
    
    register_clcmd("say /checkmath", "temp")
    register_clcmd("say /doquestion", "do_question")
}

public temp(id)
{
    if ( !is_user_admin(id) )
        return PLUGIN_HANDLED
        
    client_print(id, print_chat, "Answer = %d, question = %s", Answer, aQuestion)
    return PLUGIN_HANDLED
}

public do_question()
    Answer = analyzeAnswer()

public analyzeAnswer(){
    
    new stack[6], top
    for(new i; i<sizeof(aQuestion); i++){
        switch(aQuestion[i]){
            case '0'..'9': stack[top] = stack[top]*10+aQuestion[i]-'0'
            case '+','-','/','*','x':{
                while(top > 0 && (stack[top-1] == '*' || stack[top-1] == 'x' || stack[top-1] == '/' || aQuestion[i] == '+' || aQuestion[i] == '-')){
                    switch(stack[top-1]){
                        case '+': stack[top-2] += stack[top]
                        case '-': stack[top-2] -= stack[top]
                        case '/': stack[top-2] /= stack[top]
                        case '*','x': stack[top-2] *= stack[top]
                    }
                    top -= 2                    
                }                
                stack[++top] = aQuestion[i]            
                stack[++top] = 0                
            }
        }
    }
    while(top>0){
        switch(stack[top-1]){
            case '+': stack[top-2] += stack[top]
            case '-': stack[top-2] -= stack[top]
            case '/': stack[top-2] /= stack[top]
            case '*','x': stack[top-2] *= stack[top]
        }
        top -= 2
    }        
    
    return stack[top]
} 


Why is that? the code of analyzing is same as yours, why is not working properly? I dont spot anything.

[Sylwester]

Answer = 72, question = 9 x 2 x 4

So you probably calculated answer with different equation, then you changed equation and used command to see result without recalculating it...