Question

Application program

          Program name      PrimeNumbers.cpp

          Problem background:

                   In mathematics, a PRIME number is a number that is divisible by only

                   itself and 1.

          Examples:

                   2, 3, 5, 7, 11 are all primes

                   these are not primes

the number 4        divisible by 2

the number 6        divisible by 2 and 3

the number 12       divisible by 2, 3, 4, and 6

Write a C program to find all the prime numbers between 0 and 151

(so check the numbers from 1 ~ 150)

          Output should look like:

                   The following numbers

                     are prime numbers

                             1

                             2

                             3

                             5

                             Etc

          hint – remember the mod ( % ) operator.   X % D means that what is the remainder after X / D

                                            or

                    returns the remainder after the left operator if divided by the right operator

                    so…15%5 is 0    15%2 is 1

                    if one number divides evenly into another, the mod is 0

                   so, for a given number (say X), divide all the numbers less than X into X. If none of the

                   numbers divide evenly (the result of the % operator is 0) into X, then X is a prime

                   number.

Answer 1

Ans:-

As per Mathematics, prime number is the number greater than 1 that is divisible by itself and 1 only.

1 is not considered to be prime number.

Code:-

#include<stdio.h>
int main()
{
int l = 0,r = 151;//given values
bool k ;//boolean variable that shows whether number is prime or not. (true if prime)

printf("The following numbers are prime numbers\n");//print on screen

//run loop from given range l to r (both exclusive)
for(int i=l+1;i<r;i++)
{
k=true;//assume that number is prime
//run from 2 to number less than number to checked
for(int j=2;j<i;j++)
{
if(i%j==0)//if the number is divisible by number less than it except 1 then it is not prime
{
//if any of the number less than i divide the number evenly then
//k become false and comes out of inner loop by break statement
k = false;
break;

}
}
//1 should not be considered as prime
if(k==true && i>1)//if the number is prime.
//As per mathematics, prime number is number greater than 1 that is divisible by itself and 1 only.
{
printf("%d\n",i);//print the number followed by newline
}

}
return 0;
}

Output:-

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