C programming

Question

int main() 
{ 
    char *p="abc"; 
    char *q="abc123"; 
    while(*p++=*q++)
        printf("%c %c",*p,*q);
}

The Output is b bc c 1a 2b 3c

Here explain how did 1a 2b 3c will come as at that time p has null value

Comments

That 's what I asking why it starts iterating the first string  again after encountering the end string '\0'

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Now,I get what your problem is. I have tried to solve your problem look at the answer section.

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Kushagra can u tell me....when after first 3 comparisons null is compared to 1 ....then while loop should stop there.....Can u tell me what point am I missing

Answer 1

Instead of running the above code run the following code. This is a little modulation of your code to make your doubts clear.

int main()

{

   char*p=”abc”;

   char *q=”abc123”;

   while(*p=*q)

  {

    printf(“p=%d,q=%d”,p,q);

    printf(“\n”);

    printf(“*p=%c,*q=%c”,*p,*q);

    printf(“\n”);

    *p++;

    *q++;

    printf(“%c %c”,*p,*q);

    printf(“\n”);

   }

   }

 Output

p=100180,q=100184        

*p=a,*q=a                                          

b b  

p=100181,q=100185

*p=b,*q=b

c c

p=100182,q=100186

*p=c,*q=c

     1

p=100183,q=100187

*p=1,*q=1

a 2

p=100184,q=100188

*p=2,*q=2

b 3

p=100185,q=100189

*p=3,*q=3

c

 If you look at the outputs carefully you will find that at which address which values are stored

Address                                                     Value

100180 …………………………………………..     a

100181 …………………………………………..     b

100182…………………………………………….    c

100183……………………………………………..    null

100184 …………………………………………….    a

100185 …………………………………………….    b

100186 ……………………………………………..    c

100187 ………………………………………………    1

100188 ………………………………………………    2

100189 ……………………………………………….   3

Now your problem starts from where *p starts iterating its values (bold part of output) this is happening because at that time the value of p is 100184 and after that p= 100185 and after that p=100186 so, it takes the values a,b,c again.

I hope you will understand now.

Comments

Why *p starts iterating it's value??

And why there is 1 char memory gap between two string?? They can be allocated at any location..

 

 

Thanks

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@Rajucse,If you will talk abt the 1 char it has gotta be 1 byte specifically.And what do you meant by "allocated at any location"?A string is a collection of characters. This you already know abt  it. :). If you haven't understood still,please share your doubt in comment please.