comparing two strings

This is a discussion on comparing two strings within the C Programming forums, part of the General Programming Boards category; I want to compare two strings and see if they are the same or not Code: char myString[]="hello"; if (myString ...

  1. #1
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    comparing two strings

    I want to compare two strings and see if they are the same or not

    Code:
    char myString[]="hello";
    
    if (myString == "hello") {
    
       printf ("same\n');
    
    }
    the word same didn't appear after I run this program, is it because I am not supposed to use equal equal to compare?

    I know that in java, I have to use dot equal, what about in C?

    Or I have to do something like that:
    myString[0]='h'
    myString[1]='e'
    myString[2]='l'

    etc...?

  2. #2
    Ultraviolence Connoisseur
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    please read up on the strcmp function, you need to compare each letter of the string individually.

  3. #3
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    If you don't want to use strcmp(), the first thing you have to do is to check if the two strings have the same number of letters(you could use strlen() for this), then iterate over each letter of the two strings and check whether they are equal or not, of course if they are not equal you just have to break the loop, otherwise if they both reach the null character they are equal

  4. #4
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    The method is as follows:

    Code:
    strcmp(char String[], char String2[]);
    it returns -1 if first is before, 1 if second is before, 0 if equal

  5. #5
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    if u dont want to use strcmp() use a loop

  6. #6
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by Soulzityr
    it returns -1 if first is before, 1 if second is before, 0 if equal
    By the way, please do not rely on this. Rely only on comparison for less than, equal to, and greater than 0.
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  7. #7
    CSharpener vart's Avatar
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    Quote Originally Posted by Soulzityr View Post
    The method is as follows:

    Code:
    strcmp(char String[], char String2[]);
    it returns -1 if first is before, 1 if second is before, 0 if equal
    you are right about 0... 1 and -1 are not guaranteed
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  8. #8
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    strcmp() is not a "method" , it's a standard C function, have some respect.
    Methods are for cool boarders, and .NET'ers.

    Here are some ideas to kick around:
    Code:
    /*Yes , well a string is in a character array right?  eg: */
    #include <stdio.h>
    
    int main(void)
    {
       int i;
      char s1[] = "Hello";      
      char s2[] = { 'H', 'e', 'l', 'l', 'o', '\0', '\0', '\0' };
    
    /*
    Strings defined in double quotes are automatically appended with the null character: '\0' (zero).
    The string declarations above stored identically except that s2 will be two bytes larger.
    Their "sizes" are  6 and 8 respectively but their string lengths are  both 5. 
    */
    
      printf("sizes: s1: %u    s2: %u  \n\n", sizeof(s1),  sizeof(s2) );
    
    /*
    We "index" (number) the string characters, like any array, starting with zero.
    So you could make a loop and print the characters from index 0 until you run into the '\0':    
    */
    
      for ( i= 0; i < (int)sizeof(s2); i++ )
      {
        printf("s2[%d] = %c  %02x \n", i, s2[i], s2[i]); 
      } 
      putchar('\n');
    
    /* We could also make a loop to print the same index of both s1 and s2: */
    
      for ( i= 0; ; i++ )
      {
        /* stop when the first \0 of either string is encountered */
        if ( s1[i] == '\0' || s2[i] == '\0' )
        {
          break;
        }
        printf("s1[%d] = %c  %02x  ,  s1[%d] = %c  %02x \n", 
                                              i, s1[i], s1[i], i, s2[i], s2[i] );
      } 
    
      printf("\nThe shorter string's length is: %d \n", i );
    
      printf("\nIt doesn't take too much imagination to see how the second loop \n\
    could be used to compare two strings and calculate a meaningful value. \n\n\
    ...and from there taken to a function that returns a meaningful value! \n");
    
      return 0;
    }
    /*****  output :  ********************
    sizes: s1: 6    s2: 8  
    
    s2[0] = H  48 
    s2[1] = e  65 
    s2[2] = l  6c 
    s2[3] = l  6c 
    s2[4] = o  6f 
    s2[5] =   00 
    s2[6] =   00 
    s2[7] =   00 
    
    s1[0] = H  48  ,  s1[0] = H  48 
    s1[1] = e  65  ,  s1[1] = e  65 
    s1[2] = l  6c  ,  s1[2] = l  6c 
    s1[3] = l  6c  ,  s1[3] = l  6c 
    s1[4] = o  6f  ,  s1[4] = o  6f 
    
    The shorter string's length is: 5 
    ***********************************/
    Now try fooling around with the characters is s1 and s2....
    And yes you should look up strcmp(). Here is a nice C reference: :The C Library Reference Guide
    And NOWHERE in there are "methods" mentioned !!! whippersnappers!
    Last edited by HowardL; 03-30-2010 at 09:28 AM.

  9. #9
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    okay, sorry i used the word method. i meant function, and it does not return -1 and 1 all the time

  10. #10
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    Yes, a fancy true / false is what it returns:
    Returns zero if str1 and str2 are equal.
    Returns less than zero or greater than zero if str1 is less than or greater than str2 respectively.

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