Write a function in the program to return 1 if number is prime otherwise return 0
A prime number is natural number greater than 1 that has no positive divisors other than 1 and itself. The first few prime number are {1,3,5,7,......}
This program is not iterate through all the number starting from 2 to sqrt(N) using a for loop and for every number check if it divides N. If we find any number between 2 and sqrt(N) which divides, we return false. If we did not find not find any number between 2 and sqrt(N) which divides N then it means that N is prime and we will return true.
Why did we choose sqrt(N)?
The reason is that the smallest and greater than one factor of a number cannot be more than the sqrt of N. And we stop as soon as we find a factor. for example, if N is 49, the smallest factor is 7. For 15, smallest factor is 3.
C Program to check whether a number is prime or not
- Program:
#include<stdio.h>int main(){int i,num,p=0;printf("Please enter a number: \n");scanf("%d", &num);for(i=1; i<=num; i++){if(num % i == 0){p++;}}if(p==2){printf("Entered number is %d\n""and it is a prime number.", num);}else{printf("Entered number is %d\n""and it is not a prime number.",num);}}
- Output:
Please enter a number: 5 Entered number is 5 and it is a prime number.Or.Please enter a number: 14 Entered number is 14 and it is not a prime number.
- Visit:
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