２のｎ乗

#include <stdio.h>

int main(void)
{
    int num;
    printf("2の何乗(<=30)を求めますか？ >");
    scanf("%d",&num);
    if(num >= 31) return -1;
    printf("2^%d = %d\n",num, (1 << num));
    return 0;
}