write an iterative code for factorial in c

Sure, here is a simple iterative code for calculating factorial in C:

#include <stdio.h>

long long factorial(int n) {
    long long fact = 1;
    for(int i = 1; i <= n; i++) {
        fact *= i;
    }
    return fact;
}

int main() {
    int num;
    printf("Enter a positive integer: ");
    scanf("%d",&num);
    if (num < 0)
        printf("Error! Factorial of a negative number doesn't exist.");
    else {
        printf("Factorial of %d = %lld", num, factorial(num));
    }
    return 0;
}

This program first takes an integer input from the user. Then it checks if the number is negative, if it is, it prints an error message. If it's not, it calculates the factorial using a for loop in the factorial function and then prints the result.