小编Mic*_*wen的帖子

我很困惑如何使用指针来使这段代码工作:

#include<stdio.h>

int main(int argc, char *argv[]){

    char* test = argv[1][0];
    printf("hello %s\n", test);
}

这是错误:

incompatible integer to pointer conversion initializing
  'char *' with an expression of type 'char'; take the address with &
  [-Wint-conversion]

我知道我的代码可以得到 4 个相邻整数的正确答案。但它不适用于 13。

我唯一能想到的是它可能是一个 unsigned int 的问题，但在 Ruby 中我不认为我会遇到这个问题，因为它会自动变成一个 Bignum 类。

所以这意味着在我的计算中我错了？

请给我一个提示。

# Euler 8
# http://projecteuler.net/index.php?section=problems&id=8
# Find the thirteen adjacent digits in the 1000-digit number 
# that have the greatest product. 
# What is the value of this product? 


number = []

#split the integer as a string into an array
long_digit = "73167176531330624919225119674426574742355349194934
            96983520312774506326239578318016984801869478851843
            85861560789112949495459501737958331952853208805511
            12540698747158523863050715693290963295227443043557
            66896648950445244523161731856403098711121722383113
            62229893423380308135336276614282806444486645238749
            30358907296290491560440772390713810515859307960866
            70172427121883998797908792274921901699720888093776
            65727333001053367881220235421809751254540594752243
            52584907711670556013604839586446706324415722155397
            53697817977846174064955149290862569321978468622482
            83972241375657056057490261407972968652414535100474
            82166370484403199890008895243450658541227588666881
            16427171479924442928230863465674813919123162824586
            17866458359124566529476545682848912883142607690042
            24219022671055626321111109370544217506941658960408
            07198403850962455444362981230987879927244284909188
            84580156166097919133875499200524063689912560717606
            05886116467109405077541002256983155200055935729725
            71636269561882670428252483600823257530420752963450"

long_digit.split("").map { |s| …

我正在尝试制作一个游戏,但是我在设置属性的默认值并为每个子类设置不同的默认值时遇到问题.

这是问题所在:

class Player
   attr_accessor :hp 
   @hp = 2
end

class Harper < Player
  @hp = 5
end

bill = Harper.new.hp #=>nil

我期待它Harper.new.hp,5但它显示为nil,我不明白为什么.