I am debugging a "Guess the Number" program between 1-100. The first user creates a secretNumber and the second user guesses the number.
I'm trying to check if the second user input is a number between 1-100, but it still accepts negative numbers for some reason, and I can't figure out why.
Please note I am very new to coding, so I'm not well-versed with the jargon yet. In my class, we have just learned while loops and relational operators and if/else statements, so I am only allowed to use those.
The (secretNumber == 0) is to make sure int.TryParse() doesn't return 0 if the user typed in letters instead of numbers.
if statement checking:
( secretNumber >= 1 && secretNumber <= 100 )
and also
( secretNumber >= 1 || secretNumber <= 100 )
This is my code:
//Create a number variable to hold the whole number
int secretNumber;
//Validate that the number is a whole number AND between 1 and 100
if ( int.TryParse(secretNumberString, out secretNumber)
|| ( secretNumber >= 1 && secretNumber <= 100 )
|| secretNumber == 0 )
{
// Tell the user the problem
Console.WriteLine("Sorry, please only type in whole numbers and it must be between 1 and 100!");
// Re-ask the question
Console.WriteLine("What is your secret number?");
// Re-catch the response in the same variable
secretNumberString = Console.ReadLine();
// Re-assign the new input
int.TryParse(secretNumberString, out secretNumber);
}
The if statement should run if the user inputs a negative value.
It runs if the user types a value above 100, but it doesn't run if the value is below 100. Otherwise, it shouldn't run if the number is correctly between 1-100.
The statement must be true if the input is either non-numeric or outside 1~100 range. Is that correct?
//if string is NOT integral (notice the !) Or less than 1 Or bigger than 100
if (!int.TryParse(str, out int secretNumber) || secretNumber < 1 || secretNumber > 100)
Also, the user could still input non-integral, out-of-range number at the second attempt as it is not validated. Ideally, I believe it's better to put the validation logic as a loop variable:
string input;
int secretNumber;
do
{
Console.WriteLine("Input an integer between 1 and 100, inclusive.");
input = Console.ReadLine();
}
while (!int.TryParse(input, out secretNumber) || secretNumber < 1 || secretNumber > 100);
The problem is your || (or), this is just a simple Boolean Algebra (Propositional Logic) mistake, it needs to be && (and)
However, a similar neater pattern is a condensed validation loop
var num = 0;
Console.WriteLine("What is your secret number between 1 and 100 inclusively?");
var str = Console.ReadLine();
// while its not a number, "or" the number is less or equal to 0 "or" greater than 100
// annoy them with a message
while (!int.TryParse(str, out num ) || num <= 0 || num > 100)
{
Console.WriteLine("Omg you had one job, a number between 1 and 100 inclusively... Try again");
str= Console.ReadLine()
}
Console.WriteLine($"You won, your number is {num } ");
You might want to read the documentation for int.TryParse() — it returns true if the string was successfully parsed as an integer and false otherwise. Your test, int.TryParse( secretNumberString, out secretNumber ) || ( secretNumber >= 1 && secretNumber <= 100 ) || secretNumber == 0 ) will only ever test the value of secretNumber if the parse failed (at which point its value will be 0).
This might get you started:
static int GetAnswer( string prompt, int min , int max )
{
if (min > max) throw new ArgumentException("min must be less than or equal to max");
int value ;
bool valid = false ;
do
{
Console.WriteLine(prompt);
string answer = Console.ReadLine().Trim() ;
valid = int.TryParse(answer, out value)
&& value >= min
&& value <= max
;
if (!valid)
{
Console.WriteLine($"Sorry, please only type in whole numbers in the range {min}-{max}.");
}
} while (!valid );
return value;
}
Related
This question already has answers here:
How to elegantly check if a number is within a range?
(33 answers)
Closed 1 year ago.
Trying to check if an integer value falls into a range however it is giving me a compile time error
Operator '<=' cannot be applied to operands of type 'bool' and 'int'
int n = 3; // read from user like Convert.ToInt32(Console.ReadLine().Trim());
if ( 2 <= N <= 5)
{
Console.WriteLine("In range");
}
What is the correct way to check if a value falls into a range and why the way I wrote the check causes this error?
You can't do this:
(2<=N<=5)
You have to do it as two:
(2<=N && N<=5)
(Trying to do it as one means c# will resolve the 2<=N to some boolean, e.g true and then try to do true<=5 - this gives rise to the error that "<= cannot be used to compare a boolean to an integer")
This doesn't work they way you think it does:
(2<=N<=5)
What really happens here is the compiler first evaluates the 2<=N part of the expression as producing a boolean result. It then wants to use this boolean result for the <=5 part of the expression... and that's not allowed. C# does not let you implicitly compare a boolean with an integer, and even if it did it's doubtful the result would match your intention for the code.
Instead, you need to do this:
if( (2 <= N && N <= 5) || N > 20 )
The same applies to the 6<=N<=20 expression.
Finally, I might reduce the logic to eliminate nesting and repeated outcomes, like this:
int N = Convert.ToInt32(Console.ReadLine().Trim());
if(N % 2 !=0 || (6 <= N && N <= 20 ))
{
Console.WriteLine("Not Weird");
}
else if( (2 <= N && N <= 4) || N >20 ) //4 rather than 5, because we know N is even
{
Console.WriteLine("Weird");
}
else // N is even and <=0
{
Console.WriteLine();
}
im trying to build an algorythm which input is 10 numbers (positive and negative) and the output is the smallest positive number and the biggest negative number.
im getting the right answer for the smallest positive, but not for the biggest negative.
code and output are inserted.
If you have a collection, say, int[] numbers you can just query it with a help of Linq:
using System.Linq;
...
int[] numbers = ...
...
// Either biggest negative or 0 (if we don't have any negative values)
int biggestNegative = numbers
.Where(x => x < 0)
.DefaultIfEmpty() // <- we don't want exception on empty input
.Max();
// Either smallest positive or 0 (if we don't have any positive values)
int smallestPositive = numbers
.Where(x => x > 0)
.DefaultIfEmpty() // <- we don't want exception on empty input
.Min();
If you prefer to compute the values in a for loop:
int biggestNegative = 0;
int smallestPositive = 0;
for (int i = 0; i < 10; ++i) {
...
// Simplest, you may want to check user input
int value = int.Parse(Console.ReadLine());
...
if (value > 0)
smallestPositive = smallestPositive == 0
? value
: Math.Min(smallestPositive, value);
else if (value < 0)
biggestNegative = biggestNegative == 0
? value
: Math.Max(biggestNegativee, value);
}
Let's print the values out:
Console.WriteLine(
$"Biggest negative: {(biggestNegative == 0 ? "???" : biggestNegative.ToString())}");
Console.WriteLine(
$"Smallest positive: {(smallestPositive == 0 ? "???" : smallestPositive.ToString())}");
if (num>negMax)
There is a mistake in this condition. As your initial negMax value is 0, no negative number will meet the condition, and therefore negMax value will never be updated.
You're initializing negMax as 0.
There is no negative number that is bigger than 0.
Depending on what exactly you want to accomplish, you could do one of the following:
Initialize negMax as int.MinValue
This would be okay if it's guaranteed that there's at least one negative number, since the first negative input is guaranteed to be equal or greater. If negative input isn't guaranteed, you cannot tell if there were any and your output may end up incorrect.
Modify the condition for assigning a new value to negMax
You could instead modify the condition for assigning a new value to negMax to if (num > negMax || negMax >= 0).
Since you usually don't treat 0 as a negative number (and if you do, you can initialize negMax with any positive number instead), you'd know that there were no negative numbers if the output ends up as 0.
To do the same with posMin, you'd have to initialize it as something less than 0 and adjust the if-condition for assigning a value to that variable accordingly.
Alternatively, you could also declare negMax and posMin as int?s and check for null instead of >= 0.
If you choose this way, you can check the values for both variables and output, for example, that no negative or no positive numbers were entered instead of outputting whichever placeholder you chose.
I am trying to subtract a value from an int which has a set value. Once it gets to 0 and I subtract more from it, the value becomes negative.
I thought if I used an if-else statement to check whether the value goes below 0 it would prevent the value from becoming negative. But the value proceeds into the negative. How do I prevent the value from going into the negative range?
{
DateTime start = dateTimePicker2.Value.Date;
DateTime end = dateTimePicker1.Value.Date;
TimeSpan difference = end - start;
int days = difference.Days;
int min = 0;
int max = 21;
int rdays = Convert.ToInt32(Holidays_Number_lbl.Text);
Holidays_Number_lbl.Text = (rdays - days).ToString();
int Holidays_Number = int.Parse(Holidays_Number_lbl.Text);
if ((Holidays_Number > min) && (Holidays_Number < max))
{
MessageBox.Show("Holidays have been counted");
}
else
{
MessageBox.Show(" You have exceeded your 21 holidays ");//value goes into the minus ?
}
}
Expected result: MessageBox appears saying you have exceeded your days and value doesn't go into the negative.
Actual Result: Value proceeds into the negative.
You can specify zero as the lowest possible value with Math.Max()on the line where you do the arithmetic:
Holidays_Number_lbl.Text = (Math.Max(rdays - days, 0)).ToString();
However, you're converting to a string and then back to a number. Something like this would eliminate the need for int.Parse:
...
int Holidays_Number = Math.Max(rdays - days, 0);
Holidays_Number_lbl.Text = Holidays_Number.ToString();
if ((Holidays_Number > min) && (Holidays_Number < max))
{
...
This line int Holidays_Number = int.Parse(Holidays_Number_lbl.Text); is setting the value of Holidays_Number. Then the next line checks that with an if statement. But the if statement does not change the value, it just checks it. So if it is below 0, it will remain below 0.
I'm trying to create a program that converts a 5 digit binary number to decimal. As it stands, the conversion works perfectly, but I'm having trouble with giving an error message if the user inputs a number larger than 1.
for (int i = 4; i>=0; i--)
{
digit = txt_input.Text.Substring(i,1);
num = Convert.ToInt32(digit);
//If a digit is 1 or 0
if (num <= 1)
{
total += num * (Math.Pow(2, x));
x += 1;
goahead = 1;
}
//If a digit is not 1 or 0
if (num > 1)
{
lst_output.Items.Add("All digits must be either 1 or 0.");
i = 10;
goahead = 0;
}
}
When the user inputs 1's or 0's the program works as intended, but when a number larger than 1 is inputted, I get the error "startIndex cannot be larger than length of string" on line 3.
If a number with more or less than 5 digits is inputted, the user gets a message saying that the number must be 5 digits long. So as far as I can tell, the problem isn't the size of the startIndex. Especially since, no matter what the user inputs, startIndex remains unchanged.
Imagine your input is 10103.
Now pay attention to this part of the code:
if (num > 1)
{
lst_output.Items.Add("All digits must be either 1 or 0.");
i = 10;
goahead = 0;
}
Why are you making i = 10 here?
So if you input is the above string, in the first iteration you'd go into the if statement above, add the message to lst_output, then set i to 10. Then you go back to the for loop and the i >= 0 condition is still true so you go inside the for loop once again. Now your i = 1, but your string is of length 5.
So;
digit = txt_input.Text.Substring(i,1);
Here now you're trying to take a substring of length 1 that starts at the index = 10, from a string that is only 5 characters long.
Of course it would throw
startIndex cannot be larger than length of string.
Parameter name: startIndex.
This question already has answers here:
C# testing to see if a string is an integer?
(10 answers)
Closed 8 years ago.
//capture input value for peak size and return
public static int GetPeakSize()
{
//declare variables, intitialize and parse after input
int peak;
Console.WriteLine("\nPlease enter the peak size (must be a number 1-10): ");
peak = int.Parse(Console.ReadLine());
//if user enter anything that is not inside the 1-10 range, default
//to 3
if (peak < 1 || peak > 10)
{
peak = 3;
}
return peak;
}
In the method above I'm just trying to gather input, parse it, and if the input does not fall in the range of 1-10, return a default value of 3. But instead of just validating numerical input, I want to return a default value of 3 if ANYTHING but the numerical values of 1-10 are entered. So if they enter "four" instead of 4, I'd like the value to default to 3. I wish I could do something along the lines of if (value != int || value < 1 || value > 10)......default = 3. I know this can't be done but is there anyway around it?
You might want to use TryParse instead:
int peak;
Console.WriteLine("\nPlease enter the peak size (must be a number 1-10): ");
if (!int.TryParse(Console.ReadLine(), out peak) || peak < 1 || peak > 10)
{
peak = 3;
}
The code above will attempt to parse the input into an int -- if it could not, or if the parsed value falls outside of your range constraints, it overrides peak to 3 before continuing on.
EDIT: Missed the range constraints.
Use int.TryParse. int.Parse will throw if the input is non-numeric.
int peak = 0;
bool parseSuccess = int.TryParse(input, out peak);
if (!parseSuccess || peak < 1 || peak > 10)
{
}
int.TryParse will return false if the input is not valid, and if it is valid, then the parsed value will be contained in the "out" parameter (peak in this case).