Question

我构建了一个循环调用的程序。每次值T改变，我想比较前一个周期的值T和T，并且每个周期都这样做。

int T = externalsrc; //some external source
int prevT; //cannot do it because in the first cycle it will have no value when used in comparison
int prevT = 0; //cannot do it, because in every cycle prevT will be zero for my comparison
int comparison = prevT - T;
prevT = T;

我该如何正确地做到这一点？我也试过这个，但是T还没有在这里声明：

int T;
int prevT;
if (prevT != T)
  prevT = 0;
else
  prevT = externalsrc;
int comparison = prevT - T;
prevT = T;

Answer 1

使用您的第一个答案，但将prevT声明为static并将init声明为0：

while (condition) {
    int T = externalsrc; //some external source
    static int prevT = 0; // declaring static means that it will only be set to 0 once
    int comparison = prevT - T;
    prevT = T;
}

...在每次后续迭代中都会忽略prevT的初始化，并且从最后一次迭代中保留该值。

Answer 2

您可以保留一个布尔变量来告诉您它是否是第一次。

有些事情是这样的：

bool first_fime = true;

// ...

if (first_time)
{
    // Do something with T only
    previousT = T;

    // It's no longer the first time
    first_time = false;
}
else
{
    // Do something with both T and previousT
}

Answer 3

您可以在函数中将prevT定义为static。

您的代码将是这样的

int T = externalsrc; //some external source
int prevT; //cannot do it because in the first cycle it will have no value when used in comparison
static int prevT = 0; //The first time it is called it will start with pr
int comparison = prevT - T;
prevT = T;

Answer 4

struct compare
{
    compare() { prev = 0; }

    int operator() (int t)
    {
        int cmp;
        cmp = prev - t;
        prev = t;

        return cmp;
    }
private:
    int prev;
};

我怎样才能比较两个连续的迭代步骤？在C ++中

4 个答案: