C++ 矢量加法运算
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Vector addition operation
提问by Arpit
I am trying to add two Vectors below is the code snippet :-
我想在下面添加两个向量是代码片段：-
#include <iostream>
#include <vector>
using namespace std;
int main()
{
unsigned int i = 0;
vector <float> v1;
vector <float> v2;
vector <float> v3;
cout << "Filling the Numbers\n";
for (i=5;i < 125 ; i = i + 5) {
v1.push_back(i/10);
v2.push_back(i/100);
}
cout << "Adding the numbers\n";
for (i = 0; i < v1.size(); i++) {
v3[i] = v1[i] + v2[i];
}
cout << "Printing the numbers\n";
for (i = 0; i < v3.size() ; i++) {
cout << v3[i];
}
return 0;
}
The program is crashing at Line 18. It seems to me I need to do operator overloading for + operation. Please help.
程序在第 18 行崩溃。在我看来，我需要对 + 操作进行运算符重载。请帮忙。
回答by greyfade
To avoid the obvious pitfalls you encountered, you can do this as an alternative:
为了避免您遇到的明显陷阱，您可以这样做：
#include <algorithm> // for transform
#include <functional> // for plus
std::transform(v1.begin(), v1.end(), v2.begin(), std::back_inserter(v3), std::plus<float>());
Reference: https://en.cppreference.com/w/cpp/algorithm/transform
回答by Kornel Kisielewicz
This line doesn't work, because there's no v3[i]allocated:
此行不起作用，因为没有v3[i]分配：
v3[i] = v1[i] + v2[i];
You have two choices, either use 'push_back'
你有两个选择，要么使用'push_back'
v3.push_back( v1[i] + v2[i] );
Or resize the array to the given size before hand:
或者事先将数组调整为给定的大小：
v3.resize( v1.size() );
If you push_back, it will be nice to preallocate the space anyway:
如果你 push_back，无论如何预先分配空间会很好：
v3.reserve( v1.size() );
And finally, you can try to read up on std::valarrayinstead, as those operations are already built into it!
最后，您可以尝试继续阅读std::valarray，因为这些操作已经内置于其中！
Edit:and yes, as Johannes noted, you have a problem with floating point division :>
编辑：是的，正如约翰内斯所指出的，浮点除法有问题：>
回答by Johannes Schaub - litb
First you need to do a floating point division
首先你需要做一个浮点除法
v1.push_back(i/10.0f);
v2.push_back(i/100.0f);
Then you need to have space for ivariables on v3or use push_back
然后你需要为i变量留出空间v3或使用push_back
v3.push_back(v1[i] + v2[i]);
回答by fredoverflow
v3[i] = v1[i] + v2[i];
v3[i] = v1[i] + v2[i];
You are assigning to elements that do not exist. Try v3.push_back(v1[i] + v2[i]);instead.
您正在分配给不存在的元素。试试吧v3.push_back(v1[i] + v2[i]);。
Also, you probably want i/10.0instead of i/10, otherwise your results are rounded.
此外，您可能想要i/10.0代替i/10，否则您的结果将被四舍五入。
回答by Nils Pipenbrinck
You write into the v3 vector, but you haven't allocated any space for it.
您写入 v3 向量，但尚未为其分配任何空间。
Try to add:
尝试添加：
v3.reserve (v1.size());
between your first and second loop.
在你的第一个和第二个循环之间。
回答by bramp
I think the problem is v3[i] doesn't work as the vector starts off having zero elements. What you want to do is either:
我认为问题是 v3[i] 不起作用，因为向量开始时元素为零。你想要做的是：
v3.push_back( v1[i] + v2[i] );
or preallocate the vector
或预先分配向量
v3.resize( v1.size() );
OR the final solution, which I would do is
或者我会做的最终解决方案是
v3.reserve( v1.size() );
for (i = 0; i < v1.size(); i++) {
v3.push_back( v1[i] + v2[i] );
}
as this avoid resizing the vector again and again.
因为这样可以避免一次又一次地调整向量的大小。
