Program prints unrelated chars

Question

I wanted to split an array to 2 arrays that the first one contains the lowercased letters of the original array and the second one contains the uppercased letters and from some reason it prints some unrelated chars.

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

#define LEN 8
int main(void)
{
 char str[] = "SHaddOW";
 char smallStr[LEN], bigStr[LEN]; 
 int i = 0;
 int indexSmall = 0;
 int indexBig = 0;

 for (i = 0; i <= LEN; i++)
 {
  if (str[i] <= 'Z')
  {
   smallStr[indexSmall] = str[i];
   indexSmall++;
  }
  if (str[i] >= 'Z')
  {
   bigStr[indexBig] = str[i];
   indexBig++;
  }
 }

 printf("1: ");
 puts(smallStr);
 printf("2: ");
 puts(bigStr);

 system("PAUSE");
 return 0;
}

`i <= LEN` will exceed the bounds of `str[]` whose maximum index is `6`. It will also break the two target arrays, whose maximum index is `7`. — Weather Vane, Mar 09 '16 at 21:27
Add the line `smallStr[indexSmall] = bigStr[indexBig] = 0` to add the null character — Ed Heal, Mar 09 '16 at 21:28
Please get rid of the [system("PAUSE");](http://stackoverflow.com/a/34522206/721269) before it hurts someone. For all you know, the `PAUSE` command on my computer pauses the cooling system for my nuclear reactor. — David Schwartz, Mar 09 '16 at 21:32
@WeatherVane Oops, I miscounted OP's characters. He's got seven of them, not eight! — Sergey Kalinichenko, Mar 09 '16 at 21:41
@DavidSchwartz `system("pause")` is likely to "hurt someone"? Really? There is such a thing as unnecessary exaggeration. — user253751, Mar 09 '16 at 21:49

anita2R · Answer 1 · 2016-03-10T12:55:05.217

Don't define length before you create the string to test. Create it's length after defining the string to test.

Copy the characters as you encounter them, but as @Ed Heal says you must add a null terminator so that you can print out the two strings (they aren't really strings until they are null terminated).

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

int main (void)
{
        char str[] = "SHaddOW";
        int len = strlen(str) +1;
        char smallStr[len], bigStr[len];
        char term[] = {'\0'};
        int n, s, b;

        s=0;
        b=0;
        for(n=0; n<len; n++) {
                if(islower(str[n])) {
                        memcpy(smallStr +s,  str +n, 1);
                        s++;
                } else if (isupper(str[n])){
                        memcpy(bigStr +b,  str +n, 1);
                        b++;
                }
        }
        memcpy(smallStr + s, term, 1);
        memcpy(bigStr + b , term, 1 );

        printf("Upper: %s\n", bigStr);
        printf("Lower: %s\n", smallStr);
}

Output:

Upper: SHOW
Lower: add

Add this to the if structure (and other code to support it)

} else {
        memcpy(anyStr +a, str +n, 1);
        a++;
}

then: char str[] = ".S1H2a3d4d5O6W.";
and:
printf("Anything else: %s\n", anyStr);

returns:
Upper: SHOW
Lower: add
Anything else: .123456.

This `int len = strlen(str);` ... `char smallStr[len];` makes the array 1 space too small. — John Hascall, Mar 10 '16 at 02:35
@John Hascall - yes of course - no space for the null terminator if characters are all upper or all lower. I will correct it. — anita2R, Mar 10 '16 at 12:54

John Hascall · Answer 2 · 2016-03-10T13:15:53.747

A more compact approach with (perhaps) more meaningful variable names:

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

int main ( void ) {
    const char  str[]   = "SHaddOW";
    size_t      len     = strlen(str);    /* better to get actual length */
    char        lowers[len + 1];          /* add one for the nul char */
    char        uppers[len + 1];          /* (see below) */
    int         c;
    int         i       = 0;
    int         n_upper = 0;
    int         n_lower = 0;

    while ((c = str[i++]) != '\0') {
        if (isupper(c)) uppers[n_upper++] = c;    /* no need to reinvent */
        if (islower(c)) lowers[n_lower++] = c;    /* the wheel here */
    }
    uppers[n_upper] = '\0';                  /* the nul char ('\0') marks */
    lowers[n_lower] = '\0';                  /* the end of a C "string" */

    printf("1: %s\n", lowers);
    printf("2: %s\n", uppers);
    return 0;
}

Notes

If you are super concerned about efficiency you could add an else before if (islower...

Adding const means you "promise" the characters in the array won't be changed.

The type size_t is an integer type, but may be larger than int. It is the correct type for the return of strlen(). It is defined in <stdint.h>. None the less, using int will almost always work (on most systems a string would have to be 'yooooge' for its length to be bigger than an int can hold).

The variable c is declared as int instead of char because int is the proper type for the isXXXXX() functions (which are defined in <ctype.h>). It is also a good habit to get into because of the parallels between this loop and another common idiom while ((c = fgetc(fp)) != EOF) ....

score 0 · Answer 3 · edited Mar 10 '16 at 02:36

0

You should consider using isupper() and islower() functions. Code would be cleaner. And what if you have some non alpha characters? Your conditions won't work.

for (i = 0; i < LEN; i++)
{
    if (islower(str[i]))
    {
        smallStr[indexSmall] = str[i];
        indexSmall++;
    }
    else if (isupper(str[i]))
    {
        bigStr[indexBig] = str[i];
        indexBig++;
    }
}

As @Ed Heal mention. To avoid printing rubbish, after for loopt you should add a null characters to arrays.

smallStr[indexSmall] = '\0';
bigStr[indexBig] = '\0';

edited Mar 10 '16 at 02:36

John Hascall

9,176
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answered Mar 09 '16 at 21:31

stryku

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You missing out the nub of the problem - the null character – Ed Heal Mar 09 '16 at 21:32
You might need another go :-) – Ed Heal Mar 09 '16 at 21:49

Program prints unrelated chars

3 Answers3

Notes