**The Program in C that uses a function to determine whether a given positive integer is a fibonacci number or not is given below:**

```
#include<stdio.h>
int isFibonacci(int num) {
int a = 0, b = 1, c = a + b;
while(c < num) {
a = b;
b = c;
c = a + b;
}
return (c == num);
}
int main() {
int num;
printf("Enter a positive integer: ");
scanf("%d", &num);
if(isFibonacci(num))
printf("%d is a Fibonacci number.", num);
else
printf("%d is not a Fibonacci number.", num);
return 0;
}
```

## Output:

Enter a positive integer: 8

8 is a Fibonacci number.

## Pro-Tips**💡**

This program prompts the user to enter a positive integer, and then uses the isFibonacci function to determine if the number is a Fibonacci number or not.

The function uses a while loop to generate the Fibonacci sequence until a number greater than or equal to the input number is reached.

If the generated number is equal to the input number, the function returns 1 (true), otherwise it returns 0 (false).

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