C ++字符串混淆

Question

我想先感谢您的耐心等待。 我刚刚开始学习如何用我之前参加的101 cs课程中的一些背景知识进行编码，所以我可能会犯一些基本的错误。 这是我要解决的问题：

Find the greatest product of five consecutive digits in the 1000-digit number.

73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450

我将首先编写我收到的错误：当我调用我创建的findmax函数时，我收到以下错误：

error: could not conver '(std::string*)(&arr)' from 'std::string* {aka
  std::basic_st...}

这是我到目前为止编写的代码：

#include <iostream>
#include <string>

using namespace std;
void findmax(string test);
int main()
{
  int assignNum = 0;
  int n2;
  string p =     "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450";
  string arr[995];
  string plast = "";

  //FOR LOOP TO LIST ALL CONSECUTIVE INTEGERS OF 5 DIGITS
  for (assignNum = 0; assignNum < 995; assignNum++) {  //Sliding up initial digit
    plast = "";

    for (int j =0; j<5; j++) {

      plast = plast + p[assignNum + j];

    }
    arr[assignNum]= plast;

  }
  cout << sizeof(arr)/sizeof(arr[0]) << endl;
  findmax(arr); // THE ERROR REFERS TO HERE ******!!!!!!
}

//FIND MAX FUNCTION USING RECURSION
void findmax(string test) {
  string right="";
  int k;
  int stringSize = sizeof(test)/sizeof(test[0]);
  int middle = (sizeof(test)/sizeof(test[0]))/2;
  for (k=0; k<=stringSize; k++){
    if (test[k] >= test[middle]){
      right = right + test[k];
    }
    else {
      cout << "do nothing " << endl;
    }
    if (stringSize != 2){
      findmax(right);
    }
    else {
      if (test[0] >= test[1]){
        cout << test[0]<< endl;
        break;
      } 
      else {
        cout <<  test[1] << endl;
        break;
      }
    }
  } 
}

任何帮助将不胜感激，我已经在这方面工作了很长一段时间，真的希望它工作。

对于任何有兴趣的人，我解决了这个问题，我在开始时误解了这个问题。 这是我的代码（不试图使用递归）：

#include <iostream>
#include <string>
#include <stdio.h> /* printf, fgets */
#include <stdlib.h> /* atoi */
#include <math.h>

using namespace std;
void findmax(string test[]);
int main()
{
int assignNum = 0;
int n2;
int ntp;
int ltp = 0;
string p = "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450";

string pnew = "";

//FOR LOOP TO LIST ALL CONSECUTIVE INTEGERS OF 5 DIGITS
for (assignNum = 0; assignNum < 995; assignNum++){ //Sliding up initial digit

pnew = "";

for (int j =0; j<5; j++){

pnew = pnew + p[assignNum + j];
}

string myString = pnew;
int value = atoi(myString.c_str()); //value = 45

ntp = ((value / 10000) % 10) *((value / 1000) % 10) * ((value /100) % 10) * ((value / 10)% 10) * ((value / 1) % 10);
cout << (value / 10000) % 10 << endl;
cout << (value / 1000) % 10 << endl;
cout << (value / 100) % 10 << endl;
cout << (value / 10) % 10 << endl;
cout << (value / 1) % 10 << endl;

cout << "this is ntp: " << ntp << endl;

if (ltp>=ntp){
cout << "ltp: " << ltp << "is >= ntp: " << ntp << endl;

}
else {
cout << "ntp: " << ntp << "is > ltp: " << ltp << endl;
ltp=ntp;
}
cout << ltp << endl;
}

cout << "THE LARGEST CONSECUTIVE 5 DIGIT PRODUC IS: " << ltp << endl;

}



Answer: 40824 
execution time: .986s

Answer 1

findmax需要一个string ，但你findmax它一个string [] 。

您可以修复原型和签名：

void findmax(string test[]);
void findmax(string test[]) {

但是你在另一个地方做到了：

string right="";
// ...
findmax(right); // right is not an array

我怀疑你的意图是这样的：

std::string res = ""; // build string out of array
for (int i = 0; i < sizeof(arr)/sizeof(arr[0]); i++)
    res += arr[i];
findmax(res);

但是我遇到了分段错误，所以无论如何你的算法都有问题。

Answer 2

p是一个使用(const char *)值实例化的std :: string变量。 arr是一个std::string数组，最多可以包含995个独立的std::string值。 findmax是一个返回void的函数，它接受std::string值的副本 。 因此，当您尝试将arr传递给findmax ，只知道接受std::string的findmax的编译器在使用std::string 数组调用时会感到困惑。

您可能std::string使用char []或char *初始化的std::string感到困惑。 73167176531330624919225 ...可以被视为char arr[995]或具有适当代码修改的char *arr ，以便在调用findmax时，构造std::string对象。

PS：此外，当将非pod值传递给函数时，最好将它们作为参考传递，以避免不必要的复制：

void findmax(std::string & test)   // If you want to manipulate value in function

要么

void findmax(const std::string & test)    // To avoid surprises in client code