Persistencia

#include <stdio.h>

int persistence(int num);
int main() {
    int val = 0;
    while(val<20){
        printf("%d\n",minPersistence(val));
        val++;
    }
    getche();
}

int persistence(int num) {
    int counter=0;
    if(num<10) return 0;
    do {
        char str[20000];
        sprintf(str, "%d", num);
        num= str[0]-'0';
        int i=1;
        while (str[i] != '\0') {
            num*= str[i]-'0';
            i++;
        }
        counter++;
    }while(num>9);
    return counter;
}

int minPersistence(int num){
    int val=0;
    while(persistence(val)!=num){
        val++;
    }
    return val;
}