CODEWITHSUNDEEP
cfunction
FinalDestiny
FinalDestiny

Reputation: 1188

C function not returning the right thing?

I have a function to convert the first 3 letters of the month into a number (Jan = 1, Feb = 2, etc). 

   int convertDate(char date[3])
    {
        printf("%s", date);
        if(date == 'Ian')
            return 1;
        else
        if(date == 'Feb')
            return 2;
        else
        if(date == 'Mar')
            return 3;
        else
        if(date == 'Apr')
            return 4;
        else
        if(date == 'Mai')
            return 5;
        else
        if(date == 'Iun')
            return 6;
        else
        if(date == 'Iul')
            return 7;
        else
        if(date == 'Aug')
            return 8;
        else
        if(date == 'Sep')
            return 9;
        else
        if(date == 'Oct')
            return 10;
        else
        if(date == 'Noi')
            return 11;
        else
        if(date == 'Dec')
            return 12;
        else return 0;
    }

But, in main() when I use:

printf("%d", convertDate("Ian"));

it returns 0 instead of 1. Same for any other month. Any suggestion?

Upvotes: 2

Views: 151

Answers (6)

catchmeifyoutry
catchmeifyoutry

Reputation: 7349

Since in C string variables are of type char *, comparing strings like you do actually compares pointer adresses. Use strcmp() to compare strings instead.

Also, you could use stricmp() to do case insenstive string comparison. Note, that you could implement your function also with a loop, defining all twelve fixed strings into an array (using strncmp() to ensure that we really only compare 3 characters)

int convertDate(char date[3])
{
    const char date_names[12][4] = { 
        "Ian", "Feb", "Mar", /* etc. */ };
    int i;

    for(i = 0; i < 12; ++i)
    {
        if (strncmp(date_names[i], date, 3) == 0)
            return i+1;
    }

    return 0;
}

Upvotes: 2

Keith Thompson
Keith Thompson

Reputation: 263177

That shouldn't even compile. You're comparing a char* value (date) to an int value ('Ian').

This:

'Ian'

is not a string literal. It's a multi-character character constant, and its value is implementation-defined. It hardly ever makes sense to use it.

I'm guessing that the code you posted isn't the code you compiled. That's why you should copy-and-paste the same code that you fed to the compiler into your question.

As others have said, when comparing strings, you need to use strcmp(), not == -- which means you can't use a switch statement.

You should also be aware that the parameter declaration

char date[3]

is exactly equivalent to

char *date

The 3 is quietly ignored, and if you call dateCompare("Ianxyzfoobar"), date will point to a string with a length of 12.

Upvotes: 1

Joe
Joe

Reputation: 47609

You can't compare strings like that except in very specific circumstances (don't worry about that).

You should use strncmp, "string compare". E.g.:

#include <string.h>

then

if(strncmp(date, "Ian", 3) == 0)
            return 1;

Note using " instead of '. Using ' is entirely different, and can create a multi-byte int value on the stack, which you don't want.

Upvotes: 1

Ed Swangren
Ed Swangren

Reputation: 124632

You are performing a pointer comparison, not a string comparison. Use strcmp().

Upvotes: 0

gumik
gumik

Reputation: 623

You can't compare array of characters using == operator. Look at strcmp function.

Upvotes: 1

hmjd
hmjd

Reputation: 121961

Use strcmp() when comparing char*.

if (date == "Sep") compares the base address of the char*.

Upvotes: 5

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