If and Else statements in c not working

Question

I have made this little test program in c on my raspberry pi model b.

It compiles without errors, however, the if statement never works:

 #include <stdio.h>
 #include <unistd.h>

int main(int argc, const char * argv[])
{
    char *test = 0;
    printf("Alpha or Beta\n");
    scanf(" %s", test);
    if (test == "Alpha")
    {
        printf("This is string one test\n");
        printf("This is string two test\n");
    }
    else
    {
        printf("An error has occured\n");    
    }
    return 0;
}

For example: I will type Alpha and it will always give me the error has occurred message.

Besides the wrong string comparison, you are writing to an uninitialized pointer, `test`. — juanchopanza, May 28 '15 at 21:00
FWIW, a NULL (`0`, here)is also _considered_ invalid pointer to write to. — Sourav Ghosh, May 28 '15 at 21:03
@SouravGhosh I tried that and it said that I had a segmentation fault — benpete420, May 28 '15 at 21:10
who asked you to try writing into invalid pointer? allocate memory using `malloc()`, maybe? also, `free()` afterwards. or else, cut the crap, go for a simple array. I don't see any reason to use dynamic allocation here. — Sourav Ghosh, May 28 '15 at 21:13
refactored your code.You can check it here.use strcmp to compare strings.http://ideone.com/dbGeEy — aakansha, May 28 '15 at 21:13
@SouravGhosh No, I mean I changed the value from 0 and it gave me a segmentation fault — benpete420, May 28 '15 at 21:13
@SouravGhosh Sorry, I accidentally clicked enter. I changed it to: char test[10]; — benpete420, May 28 '15 at 21:18

score 0 · Accepted Answer · answered May 28 '15 at 20:59

0

You can't compare strings using "==". Use the strcmp function instead. http://en.cppreference.com/w/c/string/byte/strcmp

answered May 28 '15 at 20:59

rost0031

1,894
12
21

Even when I use numbers (I also changed it to int, and did all of the %d and &test and stuff like that), and it still doesn't work for me. – benpete420 May 28 '15 at 21:04
1

That's because your pointers (which is what you're checking) will not be the same since they are pointing to different memory addresses. I promise you that if/else works just fine. – rost0031 May 28 '15 at 21:06
@roost0031 would this be ok? char test[10] – benpete420 May 28 '15 at 21:10
Yes, but you have to make sure to still use strcmp() and not "==". Also, don't forget to null terminate your string. – rost0031 May 28 '15 at 21:10
Could you add a new answer with that code fixed? (If it is too much trouble I understand) – benpete420 May 28 '15 at 21:11
Why don't you give it a shot? It's your homework. You won't learn anything if I just do it for you. If you run into trouble, then ask for help. It's pretty inappropriate to ask StackOverflow to do stuff for you and you will get downvoted mercelessly. – rost0031 May 28 '15 at 21:13
Sorry, ok. (I haven't been here much). Could you please explain how comparing strings would fix my problem? – benpete420 May 28 '15 at 21:15
Because currently, the if/else will always select the else path and will always print "error has occurred". If you use the function as suggested, it should take the "if" path. – rost0031 May 28 '15 at 21:17
1

Thanks! That fixed it – benpete420 May 28 '15 at 21:20

If and Else statements in c not working

1 Answers1