Develop Reference

Nestled loops with IF statements c#

Trying to solve a simple c# question and I did but my teacher wants me to do it with a nestled loop instead of with a boolean.
Problem: Show all numbers from input number that is divisible by 3 and 7. If no number is found show "No number found".
How i solved it with bool:
Console.WriteLine("Put in a number: ");
int nummer = int.Parse(Console.ReadLine());
bool FoundLegitNumber = false;
for (int i = 1; i <= nummer; i++)
{
if (i % 3 == 0 && i % 7 == 0)
{
FoundLegitNumber = true;
Console.WriteLine($"The number {i} is evenly divisible by 3 and 7");
}
}
if (!FoundLegitNumber)
{
Console.WriteLine("Didnt find any number...");
}
How I'm trying to solve it with a for loop:
Console.WriteLine("Put in a number: ");
int nummer = int.Parse(Console.ReadLine());
for (int i = 0; i <= nummer; i++)
{
for (int j = 0; i >= j; j++)
{
if (i % 3 == 0 && i % 7 == 0)
{
Console.WriteLine($"The number {i} is evenly divisible by 3 and 7");
}
else if (j == 0)
{
Console.WriteLine("Didnt find any number...");
break;
}
}
}
I know, it doesnt make any sense but I cant figure out how to solve it. I know that I want to give J + 1 if (i % 3 == 0 && i % 7 == 0) was not true.

If you want a method that involves a nested for without distorting the basic problem, maybe you could add a dividers array like this:
int number = 21;
int[] dividers = new int[] { 3, 7 };
for (int i = 0; i <= number; i++)
{
bool matchAllDividers = true;
for (int j = 0; j < dividers.Length; j++)
{
if (i % dividers[j] != 0)
{
matchAllDividers = false;
break;
}
}
if (matchAllDividers)
{
Console.WriteLine("The number {0} is evenly divisible by all dividers".FormatWith(i));
}
else
{
Console.WriteLine("The number {0} is not evenly divisible by all dividers".FormatWith(i));
}
}

How do I print x number of integers per line and only display the odd numbers in those lines?

So far I can display the correct amount of integers per line, but I need to show only the odd numbers in the sequence. This is what I have so far:
Edited code:
for ( counter = 1; counter <= max; ++counter)
{
if( counter % 2 != 0 )
{
Console.Write(counter+"");
int printcounter = counter;
if (printcounter % 4 == 0)
{
Console.WriteLine();
}
else
{
Console.Write('\t');
}
printcounter++;
}
Console.WriteLine();
}
The output I'm getting
1
3
5
7
9
The output I'm trying to get:
1 3 5 7
9 11 13 15

Declare your printCounter variable BEFORE the loop so that it persists and correctly tracks the number of things you've printed:
public static void Main (string[] args) {
int max = 21;
int printCounter = 0;
for (int counter = 1; counter <= max; counter++)
{
if(counter % 2 != 0 )
{
Console.Write(counter + "\t");
printCounter++;
if (printCounter % 4 == 0)
{
Console.WriteLine();
}
}
}
}

You almost got it… try it like below…
int max = 100;
int printCount = 0;
for (int counter = 1; counter <= max; ++counter) {
if (counter % 2 != 0) {
Console.Write(counter + " ");
if (++printCount % 4 == 0) {
Console.WriteLine("");
}
}
}
Console.ReadKey();
Note: the line…
if (++printCount % 4 == 0) {
is shorthand for ….
printCount++;
if (printCount % 4 == 0) {
You only want to increment printCount when you print a number.

How can i reudce the number if if statments to 2 [duplicate]

This question already has answers here:
Writing FizzBuzz
(47 answers)
Closed 5 years ago.
how do I reduce the number of if statements in this code
for (int i = 1; i < number;i++)
{
if ( i % 3 == 0 && i % 5 != 0)
{
Console.WriteLine(i + " Fizz");
}
else if (i % 5 == 0 && i % 3 != 0)
{
Console.WriteLine(i + " Buzz");
}
else if(i % 3 == 0 && i % 5 == 0)
{
Console.WriteLine(i + " FizzBuzz");
}
else
{
Console.WriteLine(i);
}
}

You could do the following:
for (int i = 1; i < number;i++)
{
Console.WriteLine(string.Format("{0} {1}{2}", i, i % 3 == 0 ? "Fizz":"", i % 5 == 0 ? "Buzz":"");
}
And use no if ;-)

for (int i = 1; i < number;i++)
{
string result = i + " ";
if ( i % 3 == 0)
{
result += "Fizz";
}
if (i % 5 == 0)
{
result += "Buzz";
}
Console.WriteLine(result);
}
This would display for example 1_, 3 Fizz, 5 Buzz, 15 FizzBuzz.
See the javascript equivalent code snippet below :
var number = 20;
for (var i = 1; i < number;i++)
{
var result = i + " ";
if (i % 3 == 0)
{
result += "Fizz";
}
if (i % 5 == 0)
{
result += "Buzz";
}
document.write(result+"<br>");
}

Variables and the conditional operator can help to make code more readable:
for (int i = 1; i < number;i++)
{
bool isMod3 = i % 3 == 0;
bool isMod5 = i % 5 == 0;
string fizz = isMod3 ? "Fizz" : "";
string buzz = isMod5 ? "Buzz" : "";
string result = $"{i} {fizz}{buzz}";
Console.WriteLine(result);
}
Here's another approach that works with even more values(theoretically umlimited):
var modDict = new Dictionary<int, string> { { 3, "Fizz" }, { 5, "Buzz" } };
for (int i = 1; i < number; i++)
{
string text = string.Join("", modDict.Select(kv => i % kv.Key == 0 ? kv.Value : ""));
Console.WriteLine(i + " " + text);
}

you can try conditional operators.
(i % 3 == 0)
? (i % 5 == 0)
? Console.WriteLine(i + " FizzBuzz")
: Console.WriteLine(i + " Fizz");
: (i % 5 == 0)
? Console.WriteLine(i + " Buzz");
: Console.WriteLine(i);

Try:
string str;
for (int i = 1; i < number; i++)
{
str = i + " ";
if (i % 3 == 0)
str += "Fizz";
if (i % 5 == 0)
str += "Buzz";
Console.WriteLine(str.Trim());
}

We can do like below, but it is not good for readability
for (int i = 1; i < number; i++)
{
var x = i % 3 == 0;
var y = i % 5 == 0;
string istr = i.ToString();
string a = x ? (y ? istr + " FizzBuzz"
: istr + " Fizz")
: (y ? istr + " Buzz"
: istr);
Console.WriteLine(a);
}

string output = i % 3 == 0
? ( i % 5 != 0 ? $"{i} Fizz" : $"{i} FizzBuzz" )
: i % 5 == 0 && i % 3 != 0
? $"{i} Buzz"
: i.ToString();
Console.WriteLine( output );

Fizz buzz program wierd output?

Why does this result in 1 2 Fizz 3 ? Shouldn't it result in 1 2 Fizz?! I'am a little confused with the output of this loop..? Adding else if removes this problem,my question is why?
for (int i = 1; i <= value; i++)
{
if (i % 3 == 0)
{
ViewBag.Output += "Fizz ";
}
if (i % 5 == 0)
{
ViewBag.Output += "Buzz ";
}
else
{
ViewBag.Output += i.ToString() + " ";
}
}

You are not skipping iteration if first if matches. Thus you have else part of i % 5 if block evaluated when current i is not divided by 5:
for (int i = 1; i <= value; i++)
{
if (i % 3 == 0)
ViewBag.Output += "Fizz ";
if (i % 5 == 0)
ViewBag.Output += "Buzz ";
if ((i % 3 != 0) && (i % 5 != 0))
ViewBag.Output += i.ToString() + " ";
}
Alternative solution which uses common else block as you have it now:
for (int i = 1; i <= value; i++)
{
if (i % 3 == 0)
{
ViewBag.Output += "Fizz ";
if (i % 5 == 0)
ViewBag.Output += "Buzz ";
}
else if (i % 5 == 0)
{
ViewBag.Output += "Buzz "
}
else // neither divided by 3 nor by 5
{
ViewBag.Output += i.ToString() + " ";
}
}
And one more solution with dictionary, to avoid all this additional if...else checks:
var valuesToCheck = new Dictionary<int, string> {
{ 3, "Fizz" },
{ 5, "Buzz" }
};
for (int i = 1; i <= value; i++)
{
bool divisorFound = false;
foreach(var kvp in valuesToCheck)
{
if (i % kvp.Key == 0)
{
divisorFound = true;
ViewBag.Output += kvp.Value + " ";
}
}
if (!divisorFound)
ViewBag.Output += i + " ";
}

It is because your second if is evaluated, no matter the result of the first if.
So when i == 3, the first if evaluates to true and the second to false, and therefore the second if's else block is executed.

The second if is executed, regardless of the preceeding if so, the output you experience should be expected.
Here's a simple solution to the FizzBuzz problem lifted from a #KonradRudolph answer to a previous question
for (int i = 1; i <= value; i++)
ViewBag.Output +=
i % 15 == 0 ? "FizzBuzz " :
i % 3 == 0 ? "Fizz " :
i % 5 == 0 ? "Buzz " :
i.ToString() + " ";
or, alternatively.
string FizzBuzz(int value, int a = 3, int b = 5)
{
if value % (a * b) == 0 return "FizzBuzz";
if value % a == 0 return "Fizz";
if value % b == 0 return "Buzz";
return value.ToString();
}
used with,
viewBag.Output = string.Join(" ", Enumerable.Range(1, value).Select(FizzBuzz));
or, going beyond reason
IEnumerable<string> Checker<T>(
this IEnumerable<T> source,
params KeyValuePair<Predicate<T>, string>>[] checks)
(
var found = false;
foreach(var t int source)
{
var result =
string.Concat(checks.Where(c => c.Key(t)).Select(c => c.Value));
if (result.IsNullOrEmpty())
{
yield return t.ToString();
continue;
}
yield return result;
}
)
which could be used like this,
ViewBag.Output = string.Join(" ", Enumerable.Range(1, value).Checker(
new KeyValuePair<Predicate<T>, string>>(i => i % 3 == 0, "Fizz"),
new KeyValuePair<Predicate<T>, string>>(i => i % 5 == 0, "Buzz"));

Checking for prime number - C# logic

Here is a snippet from my code. Basically once the button is clicked this logic should fire out and determine if the number is prime or not. The problem is that some numbers are returning as "not prime", when in reality they are. Can anyone point out where the flaw is?
Thank you
private void bntTestPrime_Click(object sender, EventArgs e)
{
int num;
double num_sqrt;
int num_fl;
num = Convert.ToInt32(txtInput.Text);
num_sqrt = Math.Sqrt(num);
num_fl = Convert.ToInt32(Math.Floor(num_sqrt));
for (int i = 1; i <= num_fl; i++)
{
if (num % i == 0 && i != num)
lblResult_prime.Text = "Number " + num + " is not Prime.";
else
lblResult_prime.Text = "Number " + num + " is Prime.";
}
}

To add to Blender's answer, I'd like to point out that you're simply setting the output text on every iteration loop. That means your result will only depend upon the last number checked. What you need to do is assume the number is prime and loop through until a divisor is found. If a divisor is found. The number is prime if and only if no divisors are found. In the end the code should look something like this:
private bool IsPrime(int num)
{
double num_sqrt = Math.Sqrt(num);
int num_fl = Convert.ToInt32(Math.Floor(num_sqrt));
for (int i = 2; i <= num_fl; i++)
{
if (num % i == 0)
{
return false;
}
}
return true;
}
private void bntTestPrime_Click(object sender, EventArgs e)
{
int num = Convert.ToInt32(txtInput.Text);
bool isPrime = IsPrime(num);
if (isPrime)
lblResult_prime.Text = "Number " + num + " is Prime.";
else
lblResult_prime.Text = "Number " + num + " is not Prime.";
}

1 is a factor of every number, so you shouldn't check it. Start at 2. Also, you're already looping from 2 to sqrt(num), so there's no way for i to be equal to num.

You can decrease the performance hit on checking large numbers by using a conditional to check the first 4 primes, then start the loop at 11 and increment by 2. Something like this:
private bool IsPrime(int num)
{
double num_sqrt = Math.Sqrt(num);
int num_fl = Convert.ToInt32(Math.Floor(num_sqrt));
if (num !=1 && num !=2 && num != 3 && num != 5 && num != 7 && num % 2 > 0 _
&& num % 3 > 0 && num % 5 > 0 && num % 7 > 0)
{
for (int i = 11; i <= num_fl; i+=2)
{
if (num % i == 0)
{
return false;
}
}
}
else
return false;
return true;
}
You can shorten your code and increase the performance tremendously by using a List of primes that go big enough to cover the upper limit you want to check. Then use the Contains method to test for prime.

Try the code below.
bool IsPrime(int number) {
if(number%2==0 && number!=2) return false; //no need to check for even numbers
for (int i = 2; i < number; i++) {
if (number % i == 0 && i != number) return false;
}
return true;
}

Try this code below:
bool isPrimeNubmer(int n)
{
if (n >=0 && n < 4) //1, 2, 3 are prime numbers
return true;
else if (n % 2 == 0) //even numbers are not prime numbers
return false;
else
{
int j = 3;
int k = (n + 1) / 2 ;
while (j <= k)
{
if (n % j == 0)
return false;
j = j + 2;
}
return true;
}
}

public class PrimeChecker
{
public static bool Prime(int m)
{
for (int i =2; i< m; i++)
{
if (m % i ==0)
{
return false ;
}
}
return true;
}
public static void Main()
{
Console.WriteLine(Prime(13));
}
}