Using numbers 1, 3, 4, 6 and math operators +, -, *, / get the number 24

MathPuzzle.java

public class MathPuzzle {

    public static float getNumber(String eq)
    {
        float[] stackArray = new float[100];
        int stackPointer = 0;

        for (int i = 0; i < eq.length(); i++) {
            char c = eq.charAt(i);
            if ((c>='0') && (c<='9'))
            {
                stackArray[stackPointer] = stackArray[stackPointer]*10+(c-'0');
            }
            if (c=='+')
            {
                stackPointer--;
                stackArray[stackPointer] = stackArray[stackPointer] + stackArray[stackPointer+1];
            }
            if (c=='-')
            {
                stackPointer--;
                stackArray[stackPointer] = stackArray[stackPointer] - stackArray[stackPointer+1];
            }
            if (c=='*')
            {
                stackPointer--;
                stackArray[stackPointer] = stackArray[stackPointer] * stackArray[stackPointer+1];
            }
            if (c=='/')
            {
                stackPointer--;
                stackArray[stackPointer] = stackArray[stackPointer] / stackArray[stackPointer+1];
            }
            if (c==' ')
            {
                stackPointer++;
                stackArray[stackPointer] = 0;
            }
        }

        return stackArray[0];
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        System.out.println(getNumber("4 6/"));

        String st1 = "1346";

        String dd = "+-*/";

        for (int l = 0; l < st1.length(); l++)
            for (int m = 0; m < st1.length(); m++)
                if (m!=l)
                    for (int n = 0; n < st1.length(); n++)
                        if ((n!=l) && (n!=m))
                            for (int o = 0; o < st1.length(); o++)
                                if ((o!=l) && (o!=m) && (o!=n)) {
                                    String sss = String.format("%c %c %c %c", st1.charAt(l), st1.charAt(m), st1.charAt(n), st1.charAt(o));
                                    for (int i = 0; i < dd.length(); i++)
                                        for (int j = 0; j < dd.length(); j++)
                                            for (int k = 0; k < dd.length(); k++) {
                                                String eq = sss + dd.charAt(i) + dd.charAt(j) + dd.charAt(k);
                                                float r = getNumber(eq);
                                                if ((r>23.99) && (r<24.01))
                                                    System.out.println(eq + " " + r);
                                            }
                                }
    }

}

Solution given in reverse Polish notation