sisokuenzan

script.js

function parse(){
    var siki = document.getElementById("z").value;
    var s = {
        index:0,
        f:siki
    };

    rirekiinsert();

    document.getElementById("result").innerHTML= siki + " = " + expr(s).toString();
}

function next(s){
    s["index"]++;
    while(s["f"].charAt(s["index"])==' '){
        s["index"]++;
    }
}

function isDigit(c){
    if(('0' <= c && '9' >= c) || c == '.'){
        return 1;
    }
    return 0;
}

function num(s){
    var start = s["index"]
    if(s["f"].charAt(s["index"])=='-' || s["f"].charAt(s["index"])=='+'){
        s["index"]++;
    }
    while(isDigit(s["f"].charAt(s["index"]))){
        s["index"]++;
    }
    var end = s["index"];
    while(s["f"].charAt(s["index"])==' '){
        s["index"]++;
    }
    return parseFloat(s["f"].substring(start,end));
}

function fact(s){
    if(s["f"].charAt(s["index"]) == '('){
        next(s);
        var sum = expr(s);
        if(s["f"].charAt(s["index"]) == ')'){
            next(s);
            return sum;
        }
    }else{
        return num(s);
    }
}

function term(s){

    var sum = fact(s);

    while(s["f"].charAt(s["index"]) == '*' || s["f"].charAt(s["index"]) == '/'){
        if(s["f"].charAt(s["index"]) == '*'){
            next(s);
            sum *= fact(s);
        }else if(s["f"].charAt(s["index"]) == '/'){
            next(s);
            sum /= fact(s);
        }
        
    }
    return sum;
}

function expr(s){

    var sum = term(s);

    while(s["f"].charAt(s["index"]) == '+' || s["f"].charAt(s["index"]) == '-'){
        if(s["f"].charAt(s["index"]) == '+'){
            next(s);
            sum += term(s);
        }else if(s["f"].charAt(s["index"]) == '-'){
            next(s);
            sum -= term(s);
        }
        
    }

    return sum;
}