How do I properly compare strings in C

Question

I am trying to get a program to let a user enter a word or character  store it  and then print it until the user types it again  exiting the program  My code looks like this    include  lt stdio h gt   int main         char input 40       char check 40       int i 0      printf  Hello  nPlease enter a word or character  n        gets input       printf  I will now repeat this until you type it back to me  n         while  check    input                printf   s n   input           gets check               printf  Good bye           return 0      The problem is that I keep getting the printing of the input string  even when the input by the user  check  matches the original  input   Am I comparing the two incorrectly

User · Accepted Answer

You can t  usefully  compare strings using    or     you need to use strcmp   while  strcmp check input     0    The reason for this is because    and    will only compare the base addresses of those strings  Not the contents of the strings themselves

User · Answer

Use strcmp   This is in string h library  and is very popular  strcmp return 0 if the strings are equal  See this for an better explanation of what strcmp returns   Basically  you have to do   while  strcmp check input     0    or  while   strcmp check input     or   while  strcmp check input     You can check this  a tutorial on strcmp

User · Answer

include lt stdio h gt       include lt string h gt      int main                 char s1 50  s2 50           printf  Enter the character of strings              gets s1           printf   nEnter different character of string to repeat   n            while strcmp s1 s2                         printf   s n  s1               gets s2                     return 0          This is very simple solution in which you will get your output as you want

User · Answer

You can t compare arrays directly like this  array1  array2   You should compare them char-by-char  for this you can use a function and return a boolean  True 1  False 0  value  Then you can use it in the test condition of the while loop   Try this    include  lt stdio h gt  int checker char input   char check     int main         char input 40       char check 40       int i 0      printf  Hello  nPlease enter a word or character  n        scanf   s  input       printf  I will now repeat this until you type it back to me  n        scanf   s  check        while   checker input check                 printf   s n   input           scanf   s  check              printf  Good bye          return 0     int checker char input   char check          int i result 1      for i 0  input i     0     check i     0   i              if input i     check i                 result 0              break                      return result

User · Answer

Ok a few things  gets is unsafe and should be replaced with fgets input  sizeof input   stdin  so that you don t get a buffer overflow   Next  to compare strings  you must use strcmp  where a return value of 0 indicates that the two strings match  Using the equality operators  ie      compares the address of the two strings  as opposed to the individual chars inside them   And also note that  while in this example it won t cause a problem  fgets stores the newline character    n  in the buffers also  gets   does not  If you compared the user input from fgets   to a string literal such as  abc  it would never match  unless the buffer was too small so that the   n  wouldn t fit in it

User · Answer

Welcome to the concept of the pointer  Generations of beginning programmers have found the concept elusive  but if you wish to grow into a competent programmer  you must eventually master this concept  mdash  and moreover  you are already asking the right question  That s good   Is it clear to you what an address is  See this diagram   ----------     ----------   0x4000         0x4004        1              7     ----------     ----------   In the diagram  the integer 1 is stored in memory at address 0x4000  Why at an address  Because memory is large and can store many integers  just as a city is large and can house many families  Each integer is stored at a memory location  as each family resides in a house  Each memory location is identified by an address  as each house is identified by an address   The two boxes in the diagram represent two distinct memory locations  You can think of them as if they were houses  The integer 1 resides in the memory location at address 0x4000  think   4000 Elm St     The integer 7 resides in the memory location at address 0x4004  think   4004 Elm St      You thought that your program was comparing the 1 to the 7  but it wasn t  It was comparing the 0x4000 to the 0x4004  So what happens when you have this situation   ----------     ----------   0x4000         0x4004        1              1     ----------     ----------   The two integers are the same but the addresses differ  Your program compares the addresses

User · Answer

How do I properly compare strings    char input 40   char check 40   strcpy input   Hello       input assigned somehow strcpy check   Hello       check assigned somehow     insufficient while  check    input      good while  strcmp check  input     0     or  while  strcmp check  input       Let us dig deeper to see why check    input is not sufficient   In C  string is a standard library specification      A string is a contiguous sequence of characters terminated by and including the first null character    C11   7 1 1 1   input above is not a string   input is array 40 of char   The contents of input can become a string   In most cases  when an array is used in an expression  it is converted to the address of its 1st element     The below converts check and input to their respective addresses of the first element  then those addresses are compared   check    input      Compare addresses  not the contents of what addresses reference   To compare strings  we need to use those addresses and then look at the data they point to  strcmp   does the job     7 23 4 2     int strcmp const char  s1  const char  s2        The strcmp function compares the string pointed to by s1 to the string pointed to by s2       The strcmp function returns an integer greater than  equal to  or less than zero    accordingly as the string pointed to by s1 is greater than  equal to  or less than the string pointed to by s2    Not only can code find if the strings are of the same data  but which one is greater less when they differ     The below is true when the string differ   strcmp check  input     0     For insight  see Creating my own strcmp   function

User · Answer

Whenever you are trying to compare the strings  compare them with respect to each character  For this you can use built in string function called strcmp input1 input2   and you should use the header file called  include lt string h gt     Try this code    include lt stdio h gt    include lt stdlib h gt    include lt string h gt     int main           char s    STACKOVERFLOW       char s1 200       printf  Enter the string to be checked n     enter the input string     scanf   s  s1       if strcmp s s1   0   compare both the strings                 printf  Both the Strings match n                else               printf  Entered String does not match n                 system  pause

[c] How do I properly compare strings in C?

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