为什么程序的输出在C ++中是这样的？ [英] Why is the output of the program like this in C++?
问题描述
输入2-2-2输出junt4。
我该怎么做才能得到正确的结果？
我尝试过：
Input 2-2-2 output junt "4".
What should I do to get the correct result?
What I have tried:
#include<iostream>
using namespace std;
int i,j,k,resultt;
float a[10][10],b[10][10];
class result {
public:
// int a[10][10],b[10][10],mlt[10][10],i,j;
float mlt[10][10];
float multipication_matrices()
{
/* int i,j,k,result,mult;
for(i = 0; i < 4; ++i)
for(j = 0; j < 4; ++j)
{
mlt[i][j]=0;
} */
for(i = 0; i < 4; ++i)
for(j = 0; j < 4; ++j)
for(k = 0; k < 4; ++k)
{
resultt = mlt[i][j] = a[i][k] * b[k][j];
}
return resultt;}
}r;
int main()
{
cout << "Enter elements of matrix 1:" << endl;
for(i = 0; i < 4; ++i)
for(j = 0; j < 4; ++j)
{
cout << "Enter element a" << i + 1 << j + 1 << " : ";
cin >> a[i][j];
}
cout << "Enter elements of matrix 2:" << endl;
for(i = 0; i < 4; ++i)
for(j = 0; j < 4; ++j)
{
cout << "Enter element b" << i + 1 << j + 1 << " : ";
cin >> b[i][j];
}
cout << endl << "Output Matrix: " << endl;
for(i = 0; i < 4; ++i)
for(j = 0; j < 4; ++j)
{
cout << " " << r.multipication_matrices();
if(j == 4-1)
cout << endl;
}
return 0;
}
推荐答案
我不会上课结果。在一个直截了当（虽然天真）的实现中，我宁愿创建一个类Matrix。
I wouldn't make a classresult. In a straightforward (albeit naive) implementation I would rather make a classMatrix.
#include <iostream>
enum { N = 4 };
struct Matrix
{
int x[N][N];
void input();
void output();
};
void Matrix::input()
{
for (int r = 0; r < N; ++r)
for (int c = 0; c < N; ++c)
{
std::cout << "enter item [" << (r+1) << "][" << (c+1) "]"<< std::endl;
std::cin >> x[r][c];
}
}
void Matrix::output()
{
for (int r = 0; r < N; ++r)
{
for (int c = 0; c < N; ++c)
{
std::cout << x[r][c] << " ";
}
std::cout << std::endl;
}
}
<pre>Matrix multiply(const Matrix & a, const Matrix & b)
{
Matrix mul;
for (int r = 0; r < N; ++r)
for (int c = 0; c < N; ++c)
{
mul.x[r][c] = 0;
for (int k = 0; k < N; ++k)
mul.x[r][c] += a.x[r][k] * b.x[k][c];
}
return mul;
}
int main()
{
Matrix a,b,ab;
std::cout << "please enter the items of the first matrix" << std::endl;
a.input();
std::cout << "please enter the items of the second matrix" << std::endl;
b.input();
ab = multiply(a,b);
std::cout << "here you are the product of the matrices" << std::endl;
ab.output();
}
使用更高级的 C ++ 语言功能（例如模板你可以编写更优雅的代码。
Using more advanced C++ language features (e.g. templates) you could write more elegant code.
编译并不意味着你的代码是正确的！ ：笑：
将开发过程想象成编写电子邮件：成功编译意味着您使用正确的语言编写电子邮件 - 例如英语而不是德语 - 而不是电子邮件包含您的邮件想发送。
所以现在你进入第二阶段的发展（实际上它是第四或第五阶段，但你将在之后的阶段进入）：测试和调试。
首先查看它的作用，以及它与你想要的有何不同。这很重要，因为它可以为您提供有关其原因的信息。例如，如果程序旨在让用户输入一个数字并将其翻倍并打印答案，那么如果输入/输出是这样的：
Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.
So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.
Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:
Input Expected output Actual output
1 2 1
2 4 4
3 6 9
4 8 16然后很明显问题出在将它加倍的位 - 它不会将自身加到自身上，或者将它乘以2，它会将它自身相乘并返回输入的平方。
所以，你可以查看代码和很明显，它在某处：
Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:
int Double(int value)
{
return value * value;
}
一旦你知道可能出现的问题，就开始使用teh调试器找出原因。在你的线上设一个断点：
Once you have an idea what might be going wrong, start using teh debugger to find out why. Put a breakpoint on your line:
cout << " " << r.multipication_matrices();
并运行你的应用程序。在执行代码之前，请考虑代码中的每一行应该做什么，并将其与使用Step over按钮依次执行每一行时实际执行的操作进行比较。它符合您的期望吗？如果是这样，请转到下一行。
如果没有，为什么不呢？它有何不同？
这是一项非常值得开发的技能，因为它可以帮助你在现实世界和发展中。和所有技能一样，它只能通过使用来改善！
and run your app. Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!
尝试这样的事情：
Try something like this:
#include<iostream>
using namespace std;
class Matrix {
int** _matrix;
int nRows;
int nColumns;
public:
Matrix() : Matrix(2, 3)
{
}
Matrix(int rows, int columns)
{
nRows = rows;
_matrix = new int*[nRows];
nColumns = columns;
for (int row = 0; row < nRows; ++row)
{
_matrix[row] = new int[nColumns];
for (int column = 0; column < nColumns; ++column)
_matrix[row][column] = (row + 2) * (column + 1);
}
}
void multiply(Matrix& otherMatrix)
{
for (int row = 0; row < nRows; ++row)
{
for (int column = 0; column < nColumns; ++column)
{
_matrix[row][column] *= otherMatrix._matrix[column][row];
}
}
}
void print()
{
for (int row = 0; row < nRows; ++row)
{
for (int column = 0; column < nColumns; ++column)
{
cout << " " << _matrix[row][column] << " ";
}
cout << endl;
}
cout << endl;
}
};
int main()
{
Matrix foo(2, 3);
Matrix bar(3, 2);
cout << "foo : " << endl;
foo.print();
cout << "bar : " << endl;
bar.print();
foo.multiply(bar);
cout << "foo : " << endl;
foo.print();
cin.get();
return 0;
}
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