“在此范围中没有声明”错误

因此，我正在编写这个简单的程序，以使用发现的高斯算法来计算任何日期的日期这里。

#include <iostream>
using namespace std;

//Using the Gaussian algorithm
int dayofweek(int date, int month, int year ){
    int d=date;
    if (month==1||month==2)
        {int y=((year-1)%100);int c=(year-1)/100;}
    else
        {int y=year%100;int c=year/100;}
    int m=(month+9)%12+1;
    int product=(d+(2.6*m-0.2)+y+y/4+c/4-2*c);
    return product%7;
}

int main(){
    cout<<dayofweek(19,1,2054);
    return 0;
}

这是一个非常简单的程序，更令人困惑的是输出。

:In function  dayofweek(int, int, int)':
:19: warning:  unused variable 'y'
:19: warning: unused variable 'c'
:21: warning: unused variable 'y'
:21: warning: unused variable 'c'
:23: error: 'y' was not declared in this scope
:25: error: 'c' was not declared in this scope

它说我的变量未使用，但随后又说它未声明？

答案

变量的范围始终是它内部的块。例如，如果您做类似的事情

if(...)
{
     int y = 5; //y is created
} //y leaves scope, since the block ends.
else
{
     int y = 8; //y is created
} //y leaves scope, since the block ends.

cout << y << endl; //Gives error since y is not defined.

解决方案是定义y在if块之外

int y; //y is created

if(...)
{
     y = 5;
} 
else
{
     y = 8;
} 

cout << y << endl; //Ok

在您的程序中，您必须将 y 和 c 的定义从 if 块移至更高的范围。

//Using the Gaussian algorithm
int dayofweek(int date, int month, int year )
{
    int y, c;
    int d=date;

    if (month==1||month==2)
    {
         y=((year-1)%100);
         c=(year-1)/100;
    }
    else
    {
         y=year%100;
         c=year/100;
    }
int m=(month+9)%12+1;
int product=(d+(2.6*m-0.2)+y+y/4+c/4-2*c);
return product%7;
}

来自: stackoverflow.com

答案#

答案