recursion c prime number

1    #include<stdio.h>
2
3int isPrime(int,int);
4
5int main(){
6
7    int num,prime;
8
9    printf("Enter a positive number: ");
10    scanf("%d",&num);
11
12    prime = isPrime(num,num/2);
13
14   if(prime==1)
15        printf("%d is a prime number",num);
16   else
17      printf("%d is not a prime number",num);
18
19   return 0;
20}
21
22int isPrime(int num,int i){
23
24    if(i==1){
25        return 1;
26    }else{
27       if(num%i==0)
28         return 0;
29       else
30         isPrime(num,i-1);
31    }
32}