## My Blog List

### Check given number is prime number or not using c program

Definition of prime number: A natural number greater than one has not any other divisors except 1 and itself. In other word we can say which has only two divisors 1 and number itself.

For example: 5 Their divisors are 1 and 5.
Note: 2 is only even prime number.

Logic for prime number in c: We will take a loop and divide number from 2 to number/2. If the number is not divisible by any of the numbers then we will print it as prime number.

Example of prime numbers: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199 etc.

Find given number is prime or not:
```int main(){

int num,i,count=0;
printf("Enter a number: ");
scanf("%d",&num);
for(i=2;i<=num/2;i++){
if(num%i==0){
count++;
break;
}
}
if(count==0 && num!= 1)
printf("%d is a prime number",num);
else
printf("%d is not a prime number",num);
return 0;
}

Output:
Enter a number: 5
5 is a prime number
```
To Print Prime numbers from 1 to 100:
```int main(){
int num,i,count;

for(num = 1;num<=100;num++){
count = 0;

for(i=2;i<=num/2;i++){
if(num%i==0){
count++;
break;
}
}

if(count==0 && num!= 1)
printf("%d ",num);
}

return 0;
}

Output:
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97
```