IF ELSE syntax error within batch file?

batch-file

I'm new to batch file writing and I'm writing a script that randomly opens one of three web pages and loops after a delay. I constantly get a syntax error when I run it, but I can't pinpoint where it is.

: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

Help would be much appreciated, and thanks in advance!

Solution 1:

Here is code according to good advices of MC ND and 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

And here is the batch code following advice of 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 Single line with multiple commands using Windows batch file for an explanation of code set "location=..." & goto OpenSite.

This extra information is for rudicangiotti because of his comment below answer written by Middas.

It is not necessary for if and else with just a single command to use parentheses.

Therefore the code block

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

is parsed like

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

Perhaps this is easier to understand with C/C++ which does not require that else is on same line as command if or the closing parenthesis which belongs to the matching if.

A complete compilable C/C++ example code:

#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;
}

Also in C/C++ there is no keyword for an else if statement as the ElseIf keyword in Visual Basic or #elif directive of the preprocessor.

Therefore the above condition block could be written also as:

/* 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";
   }
}

This code block could be written in C/C++ with a lot more variants taking the different styles for brackets and indents into account.

Really interesting for batch file coding are the variants 1 to 3 whereby variant 2 shows how variant 1 should really look like if it would be possible in batch files. But nobody brackets and indents else if blocks as shown in variant 3 as with several more else if blocks inserted the last if and else would be positioned thus far to right.

IF ELSE syntax error within batch file?

Solution 1:

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