I have a calculator for finding Permutation: It displays an alert message when the value of r exceeds n.When r is less than or equal to n,its supposed to give accurate result.But its behaving absurdly. The code for the same in React.js written by me:
const PnC = () => {
const [n, setN] = useState(null);
const [r, setR] = useState(null);
const [choice, setChoice] = useState("Permutation");
const [choiceData, setChoiceData] = useState({
name: "Permutation",
});
const [result, setResult] = useState(null);
useEffect(() => {
if (choice == "Permutation")
setChoiceData({ name:"Permutation" });
else
setChoiceData({ name:"Combination" });
}, [choice]);
const handleChange = (e) => {
reset();
setChoice(e.target.value);
}
function reset() {
setN(null);
setR(null);
setResult(null);
}
function factorial(x){
var result = 1;
for (let i = 1; i <= x; i )
result *= i;
return result;
}
const calcResult = () => {
console.log(n,r);
if (choice == "Permutation") {
if (n < r)
alert("The value of n should not be less than r.Please enter valid values for n and r");
else
setResult(factorial(n) / factorial(n - r));
}
else if(choice=="Combination"){
if (n < r)
alert("The value of n should not be less than r.Please enter valid values for n and r");
else
setResult(factorial(n) / (factorial(r) * factorial(n - r)));
}
}
return (
<>
<Form>
<Form.Group className="mb-4" controlId="choice">
<Form.Label>Select the type of calculation</Form.Label>
<Form.Control
as="select"
className="select-custom-res"
onChange={(e) => handleChange(e)}
>
<option value="Permutation">Permutation</option>
<option value="Combination">Combination</option>
</Form.Control>
</Form.Group>
<Form.Group className="mb-4" controlId="text">
<Form.Text className="text">
<strong>
To find the {choiceData.name}, Enter the following values
</strong>
<br />
</Form.Text>
</Form.Group>
<Form.Group className="mb-4">
<Form.Label>Value of N</Form.Label>
<Form.Control
onChange={(e) => setN(e.target.value)}
type="number"
placeholder={"Enter the value of n"}
value={n === null ? "" : n}
/>
</Form.Group>
<Form.Group className="mb-4">
<Form.Label>Value of R</Form.Label>
<Form.Control
onChange={(e) => setR(e.target.value)}
type="number"
placeholder={"Enter the value of r"}
value={r === null ? "" : r}
/>
</Form.Group>
<Form.Group className="mb-4">
<Form.Control
readOnly
type="number"
placeholder={result === null ? "Result" : result " "}
/>
</Form.Group>
</Form>
<div className="button-custom-grp">
<Button variant="primary" onClick={calcResult}>
Calculate
</Button>
<Button variant="dark" onClick={() => reset()} type="reset">
Reset
</Button>
</div>
</>
)
}
for values like n=8,r=2
I am getting expected results, but for values like n=13,r=2
I am getting my custom alert message The value of n should not be less than r. Please enter valid values for n and r
.The same goes for Combination calculator. Why am I getting such absurd results?
CodePudding user response:
Issue
The type of n
and r
after being updated from the input is type string, not number. This isn't an issue until you attempt a numerical comparison with them.
if (n < r)
It's at this point the is a string comparison position-by-position.
console.log('"8" < "2"', "8" < "2"); // false
console.log('"13" < "2"', "13" < "2"); // true
"1"
char code is less than "2"
and so the comparison "13" < "2"
evaluates true.
Solution
Convert n
and r
to number type when updating state.
<Form.Group className="mb-4">
<Form.Label>Value of N</Form.Label>
<Form.Control
onChange={(e) => setN(Number(e.target.value))} // <-- convert to number
type="number"
placeholder={"Enter the value of n"}
value={n === null ? "" : n}
/>
</Form.Group>
<Form.Group className="mb-4">
<Form.Label>Value of R</Form.Label>
<Form.Control
onChange={(e) => setR(Number(e.target.value))} // <-- convert to number
type="number"
placeholder={"Enter the value of r"}
value={r === null ? "" : r}
/>
</Form.Group>