Assignment makes pointer from integer without cast

Question

Coming from a Java background I m learning C  but I find those vague compiler error messages increasingly frustrating  Here s my code         PURPOSE         Do case-insensetive string comparison       include  lt stdio h gt   include  lt string h gt   include  lt ctype h gt   int compareString char cString1    char cString2     char strToLower char cString      int main            Declarations     char cString1 50   cString2 50       int isEqual          Input     puts  Enter string 1          gets cString1       puts  Enter string 2          gets cString2           Call     isEqual   compareString cString1  cString2       if  isEqual    0          printf  Equal  n        else         printf  Not equal  n         return 0        WATCH OUT         This method  will  modify its input arrays  int compareString char cString1    char cString2             To lowercase     cString1   strToLower cString1       cString2   strToLower cString2           Do regular strcmp     return strcmp cString1  cString2         WATCH OUT         This method  will  modify its input arrays  char strToLower char cString             Declarations     int iTeller       for  iTeller   0  cString iTeller       0   iTeller            cString iTeller     char tolower cString iTeller         return cString      This generates two warnings    assignment makes pointer from integer without a cast   cString1   strToLower cString1   cString2   strToLower cString2    return makes integer from pointer without a cast   return cString     Can someone explain these warnings

User · Answer

1  Don t use gets  You re introducing a buffer-overflow vulnerability  Use fgets      stdin  instead  2  In strToLower you re returning a char instead of a char-array  Either return char  as Autopulated suggested  or just return void since you re modifying the input anyway  As a result  just write    nbsp    strToLower cString1    strToLower cString2      3  To compare case-insensitive strings  you can use strcasecmp  Linux  amp  Mac  or stricmp  Windows

User · Answer

You don t need these two assigments   cString1   strToLower cString1    cString2   strToLower cString2     you are modifying the strings in place   Warnings are because you are returning a char  and assigning to a char    which is equivalent to char

User · Answer

You are returning char  and not char   which is the pointer to the first character of an array    If you want to return a new character array instead of doing in-place modification  you can ask for an already allocated pointer  char   as parameter or an uninitialized pointer  In this last case you must allocate the proper number of characters for new string and remember that in C parameters as passed by value ALWAYS  so you must use char   as parameter in the case of array allocated internally by function  Of course  the caller must free that pointer later

User · Answer

strToLower s return type should be char  not char  or it should return nothing at all  since it doesn t re-allocate the string

User · Answer

As others already noted  in one case you are attempting to return cString  which is a char   value in this context - a pointer  from a function that is declared to return a char  which is an integer   In another case you do the reverse  you are assigning a char return value to a char   pointer  This is what triggers the warnings  You certainly need to declare your return values as char    not as char   Note BTW that these assignments are in fact constraint violations from the language point of view  i e  they are  errors    since it is illegal to mix pointers and integers in C like that  aside from integral constant zero   Your compiler is simply too forgiving in this regard and reports these violations as mere  warnings    What I also wanted to note is that in several answers you might notice the relatively strange suggestion to return void from your functions  since you are modifying the string in-place  While it will certainly work  since you indeed are modifying the string in-place   there s nothing really wrong with returning the same value from the function  In fact  it is a rather standard practice in C language where applicable  take a look at the standard functions like strcpy and others   since it enables  chaining  of function calls if you choose to use it  and costs virtually nothing if you don t use  chaining     That said  the assignments in your implementation of compareString look complete superfluous to me  even though they won t break anything   I d either get rid of them  int compareString char cString1    char cString2              To lowercase      strToLower cString1        strToLower cString2            Do regular strcmp      return strcmp cString1  cString2         or use  chaining  and do  int compareString char cString1    char cString2           return strcmp strToLower cString1   strToLower cString2           this is when your char   return would come handy   Just keep in mind that such  chained  function calls are sometimes difficult to debug with a step-by-step debugger   As an additional  unrealted note  I d say that implementing a string comparison function in such a destructive fashion  it modifies the input strings  might not be the best idea  A non-destructive function would be of a much greater value in my opinion  Instead of performing as explicit conversion of the input strings to a lower case  it is usually a better idea to implement a custom char-by-char case-insensitive string comparison function and use it instead of calling the standard strcmp

User · Answer

strToLower should return a char   instead of a char  Something like this would do   char  strToLower char  cString

User · Answer

char cString1     This is an array  i e  a pointer to the first element of a range of elements of the same data type  Note you re not passing the array by-value but by-pointer   char strToLower        However  this returns a char  So your assignment  cString1   strToLower cString1     has different types on each side of the assignment operator    you re actually assigning a  char   sort of integer  to an array  which resolves to a simple pointer  Due to C   s implicit conversion rules this works  but the result is rubbish and further access to the array causes undefined behaviour    The solution is to make strToLower return char

User · Answer

C strings are not anything like Java strings  They re essentially arrays of characters   You are getting the error because strToLower returns a char  A char is a form of integer in C  You are assigning it into a char   which is a pointer  Hence  converting integer to pointer    Your strToLower makes all its changes in place  there is no reason for it to return anything  especially not a char  You should  return  void  or a char    On the call to strToLower  there is also no need for assignment  you are essentially just passing the memory address for cString1    In my experience  Strings in C are the hardest part to learn for anyone coming from Java C  background back to C  People can get along with memory allocation  since even in Java you often allocate arrays   If your eventual goal is C   and not C  you may prefer to focus less on C strings  make sure you understand the basics  and just use the C   string from STL

[c] Assignment makes pointer from integer without cast

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