Thread: Different between StrA[] and StrA[20]

Hello guys, I'm new to c programming. I came across a problem when I go through a String tutorial.

Attachment 1 is and Attachment 2 shows the program and results when I run the program.
Both program are just different by StrA[] and StrA[20].

When i run the 1st program, the results that i expected is not displayed (String5).

Can anyone help me about it?
Attachment 1 shows the 1st program results and attachment 2 shows the 2nd program results

Code:

1st program
#include <stdlib.h>
#include <string.h>

void main()
{
    int strLENGTH = 0;
    char strA[] = "OPC";
    char strB[20] = "World";

    printf("String1 = %s \n",strA);
    printf("String2 = %s \n",strB);

    strLENGTH = strlen(strA);
    printf("StringLength1 = %d \n",strLENGTH);

    printf("String3 = %s \n",strA);
    printf("String4 = %s \n",strB);

    strcat(strA,strB);

    strLENGTH = strlen(strA);
    printf("StringLength2 = %d \n",strLENGTH);

    printf("String5 = %s \n",strA);
    printf("String6 = %s \n",strB);
}

Code:

2nd program
#include <stdlib.h>
#include <string.h>

void main()
{
    int strLENGTH = 0;
    char strA[20] = "OPC";
    char strB[20] = "World";

    printf("String1 = %s \n",strA);
    printf("String2 = %s \n",strB);

    strLENGTH = strlen(strA);
    printf("StringLength1 = %d \n",strLENGTH);

    printf("String3 = %s \n",strA);
    printf("String4 = %s \n",strB);

    strcat(strA,strB);

    strLENGTH = strlen(strA);
    printf("StringLength2 = %d \n",strLENGTH);

    printf("String5 = %s \n",strA);
    printf("String6 = %s \n",strB);
}

Oh... Thanks for your comment. I wish to figure out how the improper string declaration (StrA[]) will affect the subsequent lines of code.

At line 22, strcat() is used to combine both StrA and StrB. If not mistaken, the combined string (i.e. OPCWorld) should be stored in StrA.

At line 23, the displayed String5 is OPCWorld, which is expected and correct.

Then, at line 27, strlen() is used to count the length of StrA. At line 28, the displayed strLENGTH is 8, which is also expected and correct.

However, when come to line 30, String7 displayed OPC only and not OPCWorld. Kindly advice why this happens.

Originally Posted by Salem

Your program was screwed from the moment it did
strcat(strA,strB);

There's no point trying to rationalise any right/wrong/weird behaviour beyond that point.
The code is broken and needs to be fixed.

Oh, and next time, post your code between tags.
We can't copy/paste from your images.

Oh... OK, I understand. Thank You very much for your comment and help.