ç逻辑或如果 [英] C logical or in if

问题描述

我知道我不是在C非常好，但我认为，我可以得到这个权利：

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)

键入来作为的char * 和我测试过这个code。与第一部分在condition.It工作well.If我具备的条件的第二部分，我的键入包含中的这是OK，但如果所有这三个条件都可以，如果我输入走出去中，如果不是skipped.Why的是什么？

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?

推荐答案

您code：

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

等同于：

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"
      }
  }
}

的一点是，如果你有第一个的如果（）执行，如果字符串键入有东西，那么其他人永远不会执行。因为一个空字符串（中的其他部分的）不能等同于中的或出。所以，你总是有选择执行code-1，如果字符串的不为空的和无关的执行，如果字符串是空的（即长度= 0 的）。

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).

编辑：

我觉得你想要的东西一样，如果键入字符串为中，然后执行code-1，如果类型是走出去，然后执行第二个code-2。这样的：

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"   
      }
  }
}

你可以这样做：

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"
       }
}

我在这里公布了code 根据我的逻辑，它为运行：

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
:~$ 

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