Compare two strings.
  Compares string1 to string2 character by character.
  This function starts comparing the first character of each string. If they are equal to each other continues with the following pair until the characters differ or until end of string is reached.

Parameters.

string1

Null-terminated string to compare.

string2

Null-terminated string to compare.

Return Value.
  Returns a value indicating the lexicographical relation between the strings:

return value	description
<0	string1 is less than string2
0	string1 is the same as string2
>0	string1 is greater than string2

Portability.
  Defined in ANSI-C.

Example.

/* strcmp example */
#include <stdio.h>
#include <string.h>

main ()
{
  char szKey[] = "apple";
  char szInput[80];
  do {
     printf ("Which is my favourite fruit? ");
     gets (szInput);
  } while (strcmp (szKey,szInput) != 0);
  printf ("Correct answer!\n");
  return 0;
}

See also.
  strncmp, strrchr, strspn, memcmp