# Prime Number program in C

January 07, 2021

Prime numbers are the whole numbers greater than 1 and are divisible by themselves or only by the number. Example: 2, 3, 5, 7...

Program Description: prime number program in c

```    #include <stdio.h>
int main() {
int integer_number, flag = 0, i;
printf("Enter a number to check: ");
scanf("%d", &integer_number);

for (i = 2; i <= integer_number / 2; ++i) {
if (integer_number % i == 0) {
flag = 1;
break;
}
}

if (integer_number == 1) {
printf("one is neither prime nor composite");
}else {
if(flag == 0){
printf("The entered number is prime");
}else{
printf("The entered number is not prime");
}
}

return 0;
}
```

OUTPUT

Enter a number to check: 5
The entered number is prime

0 0
January 07, 2021

A prime number is a whole number that has only two factors that is 1 and the number itself. I will show you a simple algorithm to check the prime number program in C.

Algorithm

1. Input a positive integer variable Num
2. Divide the positive integer variable with (Num-1 to 2)
3. If Num is not divisible by any value, then the positive integer variable is prime, else not prime
4. Else not prime.

Implementation

```    #include <stdio.h>

int main() {
int prime;
int i, num;

printf("Enter a number: ");
scanf("%d", &num);

prime = 1;

for(i = 2; i < num; i++) {
if((num % i) == 0) {
prime = 0;
}
}

if (prime == 1){
printf("The number is prime");
}else{
printf("The number is not prime");
}
return 0;
}
```

OUTPUT

Enter a number: 5
The number is prime

0 0
July 09, 2021

A prime number is a whole number that is greater than 1 with exactly two factors. That 1 and the number itself. A prime number cannot be divided into groups of equal numbers. For example, 5 cannot be divided into groups of equal numbers. 5 can only be factorized as 1*5 and 5*1.

A prime number can calculate using tgamma function in C under the math.h header file. It works up to 20!

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

int main()
{
int num;
printf("Enter a positive number: ");
scanf("%d",&num);

num = tgamma(num + 1);

printf("%d", num);
return 0;
}
```

Output:

Enter a positive number: 5
120

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