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I have to do something like this in C. It works only if I use a char, but I need a string. How can I do this?
#define USER "jack" // jack or queen #if USER == "jack" #define USER_VS "queen" #elif USER == "queen" #define USER_VS "jack" #endif 
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We compare the strings by using the strcmp() function, i.e., strcmp(str1,str2). This function will compare both the strings str1 and str2. If the function returns 0 value means that both the strings are same, otherwise the strings are not equal.
The strcmp() compares two strings character by character. If the strings are equal, the function returns 0.
The defined( identifier ) constant expression used with the #if directive is preferred. The #ifndef directive checks for the opposite of the condition checked by #ifdef . If the identifier hasn't been defined, or if its definition has been removed with #undef , the condition is true (nonzero).
string= compares two strings and is true if they are the same (corresponding characters are identical) but is false if they are not. The function equal calls string= if applied to two strings. The keyword arguments :start1 and :start2 are the places in the strings to start the comparison.
I don't think there is a way to do variable length string comparisons completely in preprocessor directives. You could perhaps do the following though:
#define USER_JACK 1 #define USER_QUEEN 2 #define USER USER_JACK #if USER == USER_JACK #define USER_VS USER_QUEEN #elif USER == USER_QUEEN #define USER_VS USER_JACK #endif Or you could refactor the code a little and use C code instead.
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