check if number is prime (C)

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C

i want user to enter number and check if that number is prime or not

but my code show wrong result so what is wrong with my code
i know that i missed thing but do not know it

#include<stdio.h>
#include<conio.h>
int main()
    {
      int num,i,isPrime=0;
      clrscr();
      printf("please enter the number you check prime \n");
      scanf("%d",&num);
      if(num <= 1)
       printf("the number %d is not prime",num);
     else if(num == 1)
       printf("the number %d is not prime",num);
     else if(num == 2)
       printf("the number %d is prime",num);
      else{
       for(i=3;i*i<= num ;i++)
       {
         if(num % i == 0)
          {
            isPrime= 0;
            break;
          }


       }
       if( isPrime == 0)
            printf("the number %d is  prime",num);
        else
           printf("the number %d is not prime",num);
       }
       getch();
      return 0;
    }