In this post, we will learn **how to check the Prime Number using function in C** Programming language.

Any whole number which is greater than 1 and has only two factors 1 and itself is known as the **Prime Number**. For example: 2, 3, 5, 11, 47, . . . so on.

We will check whether the entered number has two or more factors using functions. If the entered number has more than two factors, then itâ€™s not a Prime Number.

So, without further ado, letâ€™s begin the tutorial.

Contents

**C Program To Check Prime Number Using Function**

// C Program To Check Prime Number Using Function #include <stdio.h> int checkPrime(int num){ int count = 0; if (num == 1){ count = 1; } for (int i = 2; i <= num / 2; i++){ if (num % i == 0){ count = 1; break; } } return count; } int main(){ int num; // Asking for Input printf("Enter a number: "); scanf("%d", &num); if (checkPrime(num) == 0){ printf("%d is a Prime Number.", num); } else{ printf("%d is not a Prime Number.", num); } return 0; }

**Output 1**

```
Enter a number: 17
17 is a Prime Number.
```

**Output 2**

```
Enter a number: 91
91 is not a Prime Number.
```

**How Does This Program Work ?**

** int num;**

In this program, we have declared an int data type variable named **num**.

** // Asking for Input
printf("Enter a number: ");
scanf("%d", &num);**

Then, the user is asked to enter a number. The value of this number will get stored in the **num** named variable.

` `** if (checkPrime(num) == 0){
printf("%d is a Prime Number.", num);
}
else{
printf("%d is not a Prime Number.", num);
}**

Then, we call a custom function named **checkPrime** which we have declared above. This function will return **0** if the entered number is **Prime** and 1 if the number is **not prime**.

If the value of **checkPrime(int num) = 0**, then the number is a Prime number and we’ll print it.Â

Otherwise the number is not a Prime Number, and we will print The entered number is not a Prime Number.

```
int checkPrime(int num){
int count = 0;
if (num == 1){
count = 1;
}
for (int i = 2; i <= num / 2; i++){
if (num % i == 0){
count = 1;
break;
}
}
return count;
}
```

We have declared a custom function named** checkPrime** which checks whether the entered number is a Prime Number or Not.

If this function returns **0** as output, then the number is a Prime Number, otherwise the entered number is not a Prime Number.

**Conclusion**

I hope after going through this post, you understand **how to check the Prime number using function in C **Programming language.

If you have any doubt regarding the program, feel free to contact us in the comment section. We will be delighted to help you.

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