this program has a problem and i dont know why ????(i think it is for cmp)

Peter_in_2780 is right, it can't be done like that. You could use this:

     if(!strcmp(p,"abcd")){
    ;
}
else if(!strcmp(p,"hello")){
    ;
}
else if(!strcmp(p,"world")){
    ;
}
else{
    ;
}

As Thaddeus suggested, you can write a huge if/else if line, or in some cases a for loop with callbacks would be a better choice.

typedef enum {
	SCN_ABCD, //"abcd"
	SCN_HELLO, //"hello"
	SCN_WORLD, //"world"
} StringChoiceNumbers;

typedef struct {
	StringChoiceNumbers eCase;
	LPCSTR szCase;
} StringChoice;

StringChoice scOptions[] = {
	{ SCN_ABCD, "abcd" },
	{ SCN_HELLO, "hello" },
	{ SCN_WORLD, "world" },
};

void ProcessStringOption(StringChoiceNumbers eOption) {
	switch (eOption) {
		case SCN_ABCD:
			//case "abcd"
			break;

		case SCN_HELLO:
			//case "hello"
			break;

		case SCN_WORLD:
			//case "world"
			break;
	}
}

//in some function that needs a switch(p) on strings
for (int i = 0; i < ARRAYSIZE(scOptions); ++i) {
	if (strcmp(scOptions[i].szCase, p) == 0) {
		ProcessStringOption(scOptions[i].eCase);
	}
}

From a processing point of view it is slower, however it improves code locality.
You may no be able to use this if you need a large number of variables from the calling function.
This can also be done without any of the enum bit and use an array of LPSTR instead of creating a structs, and just assign a plain integer to each string to simplify it a bit.

LPCSTR szOptions[] = {
	"abcd",
	"hello",
	"world",
};

void ProcessStringOption(DWORD nOption) {
	switch (nOption) {
		case 0:
			//case "abcd"
			break;

		case 1:
			//case "hello"
			break;

		case 2:
			//case "world"
			break;
	}
}

//in some function that needs a switch(p) on strings
for (int i = 0; i < ARRAYSIZE(szOptions); ++i) {
	if (strcmp(scOptions[i], p) == 0) {
		ProcessStringOption(i);
	}
}