Lowercase<-->Uppercase Function Not Working As Planned

Question

So, what I'm trying to do is create a function that switches uppercase characters to lowercase and vice-versa.

Here is what I'm working with:

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

int caplowswitch(char string[], char switched[]);

int main(){

    char name[] = "whyisthisnotworking";
    char flipped[] = "";

    caplowswitch(name, flipped);


return 0;
}

int caplowswitch(char word[], char switched[]){

    char *ptrword = word;
    unsigned short int counter = 0;

    printf("Your text input is: %s \n", word);

    while(*ptrword != NULL){

    switched[counter] = (*ptrword ^ 0x20);
    counter++;
    ptrword++;

    }

    printf("Your flipped text is: %s \n", switched);

    return 1;
}

In the process of learning. Thanks for your time.

And this doesn't work... how? should we just guess what the problem is? We're here to help, not be your debuggers. — Marc B, Feb 10 '14 at 01:09
Where do the characters you put "into" *switched* end up? (Hint: Not in the array switched/flipped, since that's only one character long.) — Hot Licks, Feb 10 '14 at 01:12

herohuyongtao · Accepted Answer · 2014-02-10T02:01:10.750

2

You forgot to add null termination to switched. You need to add

switched[counter] = '\0';  // add '\0' to the end

before

printf("Your flipped text is: %s \n", switched);

You need to change while(*ptrword != NULL) to while(*ptrword != '\0').
As @ooga pointed out, you'd better allocate enough space to flipped. So change char flipped[] = ""; to char flipped[100] = "";.

After fixing these issues, it should work as expected. Check out running result on Ideone.

edited Feb 10 '14 at 02:01

answered Feb 10 '14 at 01:20

herohuyongtao

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Thank you. I can't believe I missed that haha – Brandacus Feb 10 '14 at 01:29
Don't forget the other important points, like not allocating enough memory to `flipped` and the mistake of using `NULL` where you mean `'\0'`. – ooga Feb 10 '14 at 01:43

score 1 · Answer 2 · answered Feb 10 '14 at 01:14

You aren't giving enough space to flipped. By defining and initializing it as:

char flipped[] = "";

you are only giving it a single character, initialized to '\0', since that form of definition allocates only enough space to hold the given string, and you've passed the empty string. Try

char flipped[100] = "";

score 1 · Answer 3 · answered Feb 10 '14 at 01:21

There are three mistakes in your code.

Point1:

Never char flipped[] = ""; allocate memory like this. This is not an proper procedure.

Point2:

Dont check null character like this while(*ptrword != NULL). You should check like while(*ptrword != '\0') this.

Point3:

null termination is required for switched. So after while(*ptrword != NULL) { ...} set switched[counter]='\0'

Lowercase<-->Uppercase Function Not Working As Planned

3 Answers3