int: -2147483648~2147483647
long: -2147483648~2147483647 2147483647:linux 2038问题 打印格式 %ld unsigned long %lu
long long: -9223372036854775808 ~ 9223372036854775807 打印格式 %lld
unsigned long long:18446744073709551615 打印格式 %llu
double 打印格式:%f(带精度) %g(不带精度)