calcular factorial + numero invertido

#include <stdio.h>
int f(int a){
     int result=1,i,num;
    for(i=a;a>=1;a--){
        result=result*a;
    }
    num=dv(result);
return num;
}

int dv(int b){
    int n1,n2,n3,num1;
    n1=b%10;
    b=b/10;
    n2=b%10;
    b=b/10;
    n3=b%10;
    n1=n1*100;
    n2=n2*10;
    n3=n3*1;
    num1=n1+n2+n3;
return num1;
}

int main(){
    int n,num;
    printf("ingrese un numero\n");
    scanf("%d",&n);
    num=f(n);
    printf("el factorial invertido es: %d\n",num);

}