C logical or in if

Question

I know I'm not very good in C but I thought that I could get this right:

if(strlen(type) == 0 || strcmp(type,"in")!=0 || strcmp(type,"out")!=0)

type comes as a char* and I've tested this code with the first part of the condition.It works well.If I have the second part of the condition and my type contains "in" it's ok but if all three conditions are available,if i input "out",the if isn't skipped.Why's that?

Answer 1

your code:

if(strlen(type) == 0 || strcmp(type,"in")!=0 || strcmp(type,"out")!=0){
    " your code-1"
}
else{
    " your code-2"
}

Is equivalent to:

if(strlen(type) == 0 ){
    " your code-1"
}
else{
  if(strcmp(type,"in")!=0){
      " your code-1"   
  }
  else{
      if(strcmp(type,"out")!=0){
            " your code-1"   
      }
      else{
            " your code-2"
      }
  }
}

Point is if you have first if() executes if string type have something, then else never executes. Because a empty string(in else part) can't be equals to "in" or "out". So you always have choice to execute "code-1" if string is not empty and nothing to executes if string is empty (that is length = 0).

Edit:

I think you wants something like if type string is "in" then execute "code-1" if type is "out" then execute second code-2. like:

if(strlen(type) == 0 ){

}
else{
  if(strcmp(type,"in")!=0){
      " your code-1"   
  }
  else{
      if(strcmp(type,"out")!=0){
            " your code-2"   
      }
  }
}

you can do like:

flag = 'o';// this will save string comparison  again
if(strlen(type) == 0 || strcmp(type,"in")==0 || 
                       strcmp(type,"out")!=0 && !(flag='?')){
   "code-1"
}
else{
       if(flag=='o'){ //no strcmp needed
          "code-2"
       }
}

Here I posted a Code based on my logic and it run as:

:~$ ./a.out 
Enter string: in
in 
:~$ ./a.out 
Enter string: out
out 
:~$ ./a.out 
Enter string: xx
:~$