C Programming Tutorial 75 - Counting Prime Numbers Down From Input (Counting Prime Numbers Part 4)

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[mohitsilori]

thank you very much for this video
very informative and well explained
thank you so much

[codex]

If anyone is interested, here is my program from the last couple of videos. It identifies if the number is prime and writes it down in terms of its prime factors.

#include <stdio.h>

int main()
{
int input, i;
int sum = 0;

printf("Please enter the desired value: ");
scanf("%d", &input);

printf("%d = ", input);

int newValue = input;

if(newValue > 1)
{
for(i = 2; i <= input; i++)
{
while(newValue % i == 0)
{
sum++;
newValue = newValue / i;

if(newValue > 1)
{
* ", i);
}
else
{
i);
}


}
}

printf("\nThe amount of factors of this number is: %d\n", sum);

if(sum == 1)
{
printf("Therefore %d is a prime number.\n", input);
}
else
{
printf("Therefore %d is not a prime number.\n", input);
}
}
else
{
printf("Please enter a value higher than 1 shithead.\n");
}

return 0;
}

[HamedAdefuwa]

great course but this video really lost me, you skipped the explanation of a lot

[vicentecaballero]

How do I show how many number are prime, for example between 2 and 10 there are 4 prime numbers.

[PunmasterSTP]

Hey, we need to know about functions! If we don't, we won't be able to...function 😎

[CaptainQ]

So when I write my function isPrime if it is located below the main and I try to compile it wont compile and if I move it above the main it works fine, any idea why?

[tiagodmota]

My code:

#include <stdio.h>
#include <stdbool.h>
#include <math.h>

bool testPrime(int input); //function prototype

int main(void)
{
int primeNumRange;

printf("You wanna see the primes from: ");
if(scanf("%d", &primeNumRange) == false) /*it checks if the input is an int (scanf function returns 0 if the input is different of int)*/
{
printf("\n<<<Invalid Entry>>>\n\n");
return 0;
}

if(primeNumRange < 2)
{
printf("\n<<There isn't prime numbers from 1 to minus infinite>>\n\n");
return 0;
}

printf("\nPrime numbers from %d to 0:\n\n", primeNumRange);

for(int i = primeNumRange; i > 1; i--)
{
bool isPrime = testPrime(i);

if( isPrime && (i > 2) )
{
printf("%d, ", i);
}
else if (i == 2) //To put a dot "." at the end, and not a comma ", "
{
printf("%d.", i);
}
}

printf("\n\n");

return 0;
}

bool testPrime(int input)
{
for(int i = sqrt(input); i > 1; i--)
{
if ((input % i) == 0)
{
return false;
}
}

return true;
}

[AniketRana-ho]

Please give me the code of all Armstrong number 1 to n

[aritora]

I just wanted to ask one thing that when ever I write 1. It says that 1 is a prime number.. which is not.. so how to fix this issue? Thanks for uploading this.. Please answer it..