批处理文件中的 IF ELSE 语法错误？

我是批处理文件写入的新手，我正在编写一个脚本，该脚本随机打开三个网页之一并在延迟后循环。当我运行它时，我经常遇到语法错误，但我无法确定它在哪里。

:main
@echo on
set location=""
set /A num=%random% %% 10 
if /A"%num%"=="0"
(
    set location="yahoo.com"
) 
else if /A"%num%"=="1"
(
    set location="msn.com"
)
else
(
    set location="google.com"
)

start "Chrome" chrome --new-window %location%
timeout /t 30 /nobreak >NUL
goto main

非常感谢您的帮助，并提前致谢！

这是根据良好建议的代码MC ND https://stackoverflow.com/users/2861476/mc-nd and Magoo https://stackoverflow.com/users/2128947/magoo:

@echo off
:main
set location=
set /A num=%random% %% 10
if "%num%"=="0" (
   set "location=yahoo.com"
) else if "%num%"=="1" (
   set "location=msn.com"
) else (
   set "location=google.com"
)
start "Chrome" chrome.exe --new-window "%location%"
timeout /t 30 /nobreak >NUL
goto main

这是遵循建议的批处理代码Ed Heal https://stackoverflow.com/users/892256/ed-heal:

@echo off
:main
set location=
set /A num=%random% %% 10
if "%num%"=="0" set "location=yahoo.com" & goto OpenSite
if "%num%"=="1" set "location=msn.com"   & goto OpenSite
set "location=google.com"
:OpenSite
start "Chrome" chrome.exe --new-window "%location%"
timeout /t 30 /nobreak >NUL
goto main

See 使用 Windows 批处理文件的单行多个命令 https://stackoverflow.com/q/25343351代码的解释set "location=..." & goto OpenSite.

此额外信息适用于鲁迪奇安奥蒂 https://stackoverflow.com/users/3837788/rudicangiotti因为他在下面的回答中发表了评论Middas https://stackoverflow.com/users/1309672/middas.

没有必要if and else只需一个命令即可使用括号。

因此代码块

if "%num%"=="0" (
   set "location=yahoo.com"
) else if "%num%"=="1" (
   set "location=msn.com"
) else (
   set "location=google.com"
)

被解析为

if "%num%"=="0" (
   set "location=yahoo.com"
) else (
   if "%num%"=="1" (
      set "location=msn.com"
   ) else (
      set "location=google.com"
   )
)

也许用 C/C++ 更容易理解，因为它不需要else与命令在同一行if或属于匹配的右括号if.

完整的可编译C/C++示例代码：

#ifdef __cplusplus
#include <cstdio>    /* printf */
#include <cstdlib>   /* rand   */
#include <cstring>   /* strcmp */
#else
#include <stdio.h>   /* printf */
#include <stdlib.h>  /* rand   */
#include <string.h>  /* strcmp */
#endif

int main (int argc, char* argv[])
{
   const char* sLocation;
   int iNum = rand() % 10;

   if(iNum == 0) sLocation = "yahoo.com";
   else if(iNum == 1) sLocation = "msn.com";
   else sLocation = "google.com";
   printf("Number is %d and location is \"%s\".\n",iNum,sLocation);

   /* Some not really useful code to avoid warnings. */
   if(argc > 1)
   {
      if(!strcmp(argv[1],"/?"))
      {
         printf("There is no help for this small demo application.\n");
      }
   }
   return 0;
}

同样在 C/C++ 中，没有关键字else if声明为ElseIfVisual Basic 中的关键字或#elif预处理器的指令。

因此上面的条件块也可以写成：

/* Variant 1: Same usage of brackets and indents like in first batch example. */
if(iNum == 0) {
   sLocation = "yahoo.com";
} else if(iNum == 1) {
   sLocation = "msn.com";
} else {
   sLocation = "google.com";
}

/* Variant 2: Same usage of brackets like in first batch example,
   but this time with indents as it would be 100% correct according
   to processing. It is not possible to use this syntax in batch
   files because the second if must be on same line as first else. */
if(iNum == 0) {
   sLocation = "yahoo.com";
} else
   if(iNum == 1) {
      sLocation = "msn.com";
   } else {
      sLocation = "google.com";
   }

/* Variant 3: Same usage of brackets like in second batch example,
   but without omitting not necessary brackets for first else block. */
if(iNum == 0) {
   sLocation = "yahoo.com";
} else {
   if(iNum == 1) {
      sLocation = "msn.com";
   } else {
      sLocation = "google.com";
   }
}

/* Variant 4: One more variant not possible in batch file,
   but using a very common style for C/C++ programmers. */
if(iNum == 0)
{
   sLocation = "yahoo.com";
}
else if(iNum == 1)
{
   sLocation = "msn.com";
}
else
{
   sLocation = "google.com";
}

/* Variant 5: This is variant 3 in coding style of variant 4. */
if(iNum == 0)
{
   sLocation = "yahoo.com";
}
else
{
   if(iNum == 1)
   {
      sLocation = "msn.com";
   }
   else
   {
      sLocation = "google.com";
   }
}

该代码块可以用 C/C++ 编写，并具有更多变体，考虑到括号和缩进的不同样式。

对于批处理文件编码来说，真正有趣的是变体 1 到 3，其中变体 2 显示了变体 1 如果可以在批处理文件中实现的话，应该是什么样子。但没有人加括号和缩进else if如变体 3 所示的块以及其他几个块else if最后插入的块if and else到目前为止将位于右侧。