Error: 'else' without a previous "if' even though there is not a semicolon

Question

我做了一个非常简单的程序，但是即使没有分号，我仍然会出现这个错误。请无视本节目的诡异意图，纯属搞笑。

#include <iostream>
#include <cstdlib>
using namespace std;
int main()
{
    int john, jeff, philip, joe, dave;
    cout << "Hello and welcome to the blessing service" << endl;
    cout << "please enter your name and god will" << endl;
    cout << "decide if you are cursed or blessed" << endl;
    cout << "______________________________________" << endl;
    cin >> john, jeff, philip, joe, dave;
    if (john, jeff, philip, joe, dave)
        cout << "you have been cursed, you will have bad luck" << endl;
        cout << "for the rest of your life!" << endl;
    else
        cout << "you have been blessed, enjoy your life" << endl;
        cout << "and keep praying to God" << endl;
    system ("pause");
    return 0;
}

Answer 1

此代码

if (john, jeff, philip, joe, dave)
    cout << "you have been cursed, you will have bad luck" << endl;
    cout << "for the rest of your life!" << endl;
else
    cout << "you have been blessed, enjoy your life" << endl;
    cout << "and keep praying to God" << endl;
system ("pause");

实际上是

if (john, jeff, philip, joe, dave)
    cout << "you have been cursed, you will have bad luck" << endl;
cout << "for the rest of your life!" << endl;
else
    cout << "you have been blessed, enjoy your life" << endl;
cout << "and keep praying to God" << endl;
system ("pause");

缩进对c++没有意义，你需要

if (john, jeff, philip, joe, dave){
    cout << "you have been cursed, you will have bad luck" << endl;
    cout << "for the rest of your life!" << endl;
} else {
    cout << "you have been blessed, enjoy your life" << endl;
    cout << "and keep praying to God" << endl;
}
system ("pause");

它也不太可能让 cin 和 if 做你想做的事。我怀疑您正在尝试测试某人的名字是 John 还是 Jeff 等等

在那种情况下你需要

    string name;
    cin >> name;

然后

    if(name=="Jeff"||name = "John||name ==......)

Answer 2

由于您没有在 if 代码主体周围使用 {}，因此编译器会像下面这样读取您的代码：

#include <iostream>
#include <cstdlib>
using namespace std;
int main()
{
    int john, jeff, philip, joe, dave;
    cout << "Hello and welcome to the blessing service" << endl;
    cout << "please enter your name and god will" << endl;
    cout << "decide if you are cursed or blessed" << endl;
    cout << "______________________________________" << endl;
    cin >> john, jeff, philip, joe, dave;
    if (john, jeff, philip, joe, dave)
    {
        cout << "you have been cursed, you will have bad luck" << endl;
    }
        cout << "for the rest of your life!" << endl;
    else
    {
        cout << "you have been blessed, enjoy your life" << endl;
    }
        cout << "and keep praying to God" << endl;
    system ("pause");
    return 0;
}

您应该执行以下操作：

#include <iostream>
#include <cstdlib>
using namespace std;
int main()
{
    int john, jeff, philip, joe, dave;
    cout << "Hello and welcome to the blessing service" << endl;
    cout << "please enter your name and god will" << endl;
    cout << "decide if you are cursed or blessed" << endl;
    cout << "______________________________________" << endl;
    cin >> john, jeff, philip, joe, dave;
    if (john, jeff, philip, joe, dave)
    {
        cout << "you have been cursed, you will have bad luck" << endl;
        cout << "for the rest of your life!" << endl;
    }
    else
    {
        cout << "you have been blessed, enjoy your life" << endl;
        cout << "and keep praying to God" << endl;
    }
    system ("pause");
    return 0;
}

Answer 3

此表达式语句中的初学者

cin >> john, jeff, philip, joe, dave;

使用了逗号运算符。相当于

( cin >> john ), ( jeff ), ( philip ), ( joe ), ( dave );

所以第一个操作数之后的所有操作数

( jeff ), ( philip ), ( joe ), ( dave )

不产生任何影响。

你的意思好像是

cin >> john >> jeff >> philip >> joe >> dave;

再次在这个if语句的条件下

if (john, jeff, philip, joe, dave)

使用了具有相同逗号运算符的表达式。表达式的值是最后一个操作数 dave 上下文转换为 bool 类型的值。

不清楚您要在此 if 语句中检查什么。

尽管如此，下面的一对语句应该包含在像

这样的复合语句中

if (john, jeff, philip, joe, dave)
{
    cout << "you have been cursed, you will have bad luck" << endl;
    cout << "for the rest of your life!" << endl;
}
else
{
    cout << "you have been blessed, enjoy your life" << endl;
    cout << "and keep praying to God" << endl;
}

你的意思好像是下面这样

#include <iostream>
#include <string>
#include <cstdlib>

using namespace std;

int main()
{
    string name;

    cout << "Hello and welcome to the blessing service" << endl;
    cout << "please enter your name and god will" << endl;
    cout << "decide if you are cursed or blessed" << endl;
    cout << "______________________________________" << endl;

    cin >> name;

    if (name == "john" || name == "jeff" || name == "philip" || name == "joe" || name == "dave")
    {
        cout << "you have been cursed, you will have bad luck" << endl;
        cout << "for the rest of your life!" << endl;
    }
    else
    {
        cout << "you have been blessed, enjoy your life" << endl;
        cout << "and keep praying to God" << endl;
    }

    system ("pause");

    return 0;
}

if语句中的条件可以随意更改。

Error: 'else' without a previous "if' even though there is not a semicolon

Error: 'else' without a previous "if' even though there is not a semicolon

c++

if-statement

comma-operator