具有多个变量初始化的 C++ for 循环结构
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C++ for-loop structure with multiple variable initialization
提问by jdphenix
On the 2nd for-loop, I get the following error from gcc:
在第二个 for 循环中，我从 gcc 收到以下错误：
error: expected unqualified-id before 'int'
I'm not sure what I'm missing. I've looked over documentation for how a for-loop should look and I'm still confused. What's wrong here?
我不确定我错过了什么。我查看了有关 for 循环外观的文档，但我仍然感到困惑。这里有什么问题？
#include <iostream>
#include <vector>
int main() {
std::vector<int> values;
for (int i = 0; i < 20; i++) {
values.push_back(i);
}
std::cout << "Reading values from 'std::vector values'" << std::endl;
for (int i = 0, int col = 0; i < values.size(); i++, col++) {
if (col > 10) { std::cout << std::endl; col == 0; }
std::endl << values[i] << ' ';
}
}
回答by jweyrich
Try without the intbefore col.
尝试没有intbefore col。
for (int i = 0, col = 0; i < values.size(); i++, col++)
for (int i = 0, col = 0; i < values.size(); i++, col++)
回答by Jerry Coffin
Others have already told you how to fix the problem you've noticed. On a rather different note, in this:
其他人已经告诉您如何解决您注意到的问题。在一个相当不同的注释中，在此：
if (col > 10) { std::cout << std::endl; col == 0; }
It seems nearly certain that the last statement here: col==0;is really intended to be col=0;.
几乎可以肯定，这里的最后一个语句:col==0;真的打算是col=0;.
回答by Chethan Ravindranath
This should fix it
这应该解决它
for (int i = 0, col = 0; i < values.size(); i++, col++) {
if (col > 10) { std::cout << std::endl; col == 0; }
std::endl << values[i] << ' ';
}
}
A variable definition goes like this
一个变量定义是这样的
datatype variable_name[=init_value][,variable_name[=init_value]]*;
数据类型 variable_name[=init_value][,variable_name[=init_value]]*;
回答by Kalpesh Patel
Don't declare int after comma use,
不要在逗号使用后声明 int，
for (int i = 0,col = 0; i < values.size(); i++, col++) {
if (col > 10) { std::cout << std::endl; col == 0; }
std::endl << values[i] << ' ';
}
}
回答by def
This is akin to a regular multiple variables declaration/initialization in one line using a comma operator. You can do this:
这类似于使用逗号运算符在一行中进行常规的多变量声明/初始化。你可以这样做：
int a = 1, b = 2;
declaring 2 ints. But not this:
声明 2 个整数。但不是这个：
int a = 1, int b = 2; //ERROR
