Thread: Char arrays

I really need help with this one. Very confused with arrays... I always get FALSE in this program. How to make them match?
Source:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
 

int main()
{
    char array1[10],array2[10],array3[10];
    array1[10]='h','e';
    
    array2[10]='l','l','o';
    array3[10]='h','e','l','l','o';
    if(((array1,array2)==array3)==TRUE) 
    {
                                      printf("THEY MATCH"); 
                                      system("PAUSE");
                                      }
                                      if(((array1,array2)==array3)==FALSE)
                                      {
                                                                        printf("THEY DONT MATCH");
                                                                        system("PAUSE");
                                                                        }
                                                                        }

Give a look to:
strcat - C++ Reference
strcmp - C++ Reference

What are you even trying to do with this code? I'm quite sure (array1,array2) doesn't do what you think, and you can't compare arrays with ==, you need to compare them element-by-element (e.g. for loop).

windows.h and system("PAUSE") are OS-specific, it's best to avoid them where possible. After I fixed that, here's what I got when I compiled:

Code:

$ make arr
gcc -Wall -ggdb3 -pedantic -std=c99 -O0 -o arr arr.c -lm -lpthread -lrt
arr.c: In function ‘main’:
arr.c:11:49: warning: left-hand operand of comma expression has no effect [-Wunused-value]
arr.c:14:16: warning: left-hand operand of comma expression has no effect [-Wunused-value]
arr.c:19:16: warning: left-hand operand of comma expression has no effect [-Wunused-value]

You should see similar warnings. If not, turn the warning level up on your compiler. The "comma expression" is (array1,array2).


Even if it the comma operator did concatenate arrays, array1 and array2 are each 10 chars, so your comparison would fail since there would be 8 garbage values between the 'h', 'e' in array1 and the 'l', 'l', 'o' in array2. Neither are array1, array2 or array3 strings since they are missing the null terminator that C requires on all strings, so functions like strcat and strcmp would also not work.

As for (array1,array2), that expression yields array2, so

Code:

(array1,array2)==array3
// is reduced to
array2==array3

Also, the language will let you compare, e.g., array1 == array2, but it does not do what you think. When you use an array name without any [ ] brackets, it gives you a pointer to the first element. Thus, array1 == array2 checks if the first element of array1 is in the same memory location as the first element of array2. Since they're different arrays, and occupy different spots in memory, it will always be false.

I suggest getting a couple good books, and finding some online tutorials, and reading the array sections carefully. Work through all the practice problems you can find. Even copy the example programs from the books, and try changing small pieces to see what happens.

Originally Posted by std10093

cut

My idea for doing the test was:

Code:

#include <stdio.h>
#include <string.h>


int main(void){


   char array1[10]="he";

   char array2[10]="llo";

    char array3[10]="hello";


    if(!strcmp(strcat(array1,array2),array3)){
        printf("THEY MATCH\n");
    }
    else{
        printf("THEY DONT MATCH\n");
    }

    return 0;   
}

But to be pedantic, in this way OP changes the array1 content, so he should create a new array and use strcpy as you suggest.