﻿ C Program: Check whether a given number is prime or not - w3resource

# C Exercises: Check whether a given number is prime or not

## C For Loop: Exercise-32 with Solution

Write a C program to determine whether a given number is prime or not.

Visual Presentation: Sample Solution:

C Code:

``````#include <stdio.h> // Include the standard input/output header file.

int main() {
int num, i, ctr = 0; // Declare variables for user input, loop control, and a counter.

// Prompt the user to input a number.
printf("Input a number: ");
scanf("%d", &num); // Read the input number from the user.

// Start a loop to check for factors of the input number.
for (i = 2; i <= num / 2; i++) {
if (num % i == 0) { // If the input number is divisible by 'i'.
ctr++; // Increment the counter.
break; // Exit the loop since a factor has been found.
}
}

// If no factors were found and the number is not 1.
if (ctr == 0 && num != 1)
printf("%d is a prime number.\n", num); // Print that the number is prime.
else
printf("%d is not a prime number.\n", num); // Print that the number is not prime.

return 0; // Return 0 to indicate successful execution.
}

```
```

Sample Output:

```Input  a number: 13
13 is a prime number.
```

Flowchart: C Programming Code Editor:

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