Display short form of a string

Question

I am a beginner in C programming. I recently tried solving a simple problem to find the short form of a string. I can't understand why we are using *(ptr+i-1) in the program. What if I use only * (ptr+i). Can anyone please tell me how this works?

#include<stdio.h>
#include<string.h>
int main()
{
    char sent[100];
    char *ptr;
    printf("Enter a sentence : ");
    gets(sent);

    char len=strlen(sent);
    printf("%c",*sent);
    ptr=&sent;
    for(int i=1; i<len; i++)
    {
        if(*(ptr+i-1) == ' ')
        {
            printf(" %c",*(ptr+i));
        }
    }
    return 0;
}

You're looking for a space character one character before the index. Marks the beginning of a new word. — Fiddling Bits, May 08 '20 at 16:52
This looks like C, not C++. In C++ you'd use `std::string`s rather than C-style arrays of `char`. — Jesper Juhl, May 08 '20 at 16:53
".. what if i use only `* (ptr+i)` .." – that's the great thing, you can actually go ahead and try it. — Jongware, May 08 '20 at 16:54
The whole ditto code copied from [here](https://cod3addicts.wordpress.com/2012/01/14/c-program-to-make-abbreviation-of-a-string/). — Rohan Bari, May 08 '20 at 16:58
The thing with `*(ptr+i-1)` is that it is how beginners write what seasoned C programmers would write as `ptr[i-1]`. Likewise `*(ptr+i)` is just `ptr[i]`. — Antti Haapala -- Слава Україні, May 08 '20 at 16:59
[Never use `gets()`](https://stackoverflow.com/tags/gets/info). — Keith Thompson, May 08 '20 at 17:04
@LinuXMan: it is alright (-ish) to ask about existing code. But asking "how does `a+b-1` works" is at the low end of "what's there to understand about?" — Jongware, May 08 '20 at 17:04

RobertS supports Monica Cellio · Answer 1 · 2020-05-08T17:01:10.447

2

"I can't understand why we are using *(ptr+i-1) in the program. What if I use only * (ptr+i). Can anyone please tell me how this works?"

for(int i=1; i<len; i++)
{
    if(*(ptr+i-1) == ' ')
    {
        printf(" %c",*(ptr+i));
    }
}

*(ptr+i-1) is important as i is starting by/ initialized to 1 not 0 regarding reading the string from its first character, not the second.

With *(ptr+i) you would read from the second character of the string instead.

Side note:

gets(sent); -> Don´t use gets(), it is deprecated:

Why is the gets function so dangerous that it should not be used?

edited May 08 '20 at 17:01

answered May 08 '20 at 16:58

RobertS supports Monica Cellio

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If I started the i=0, what will be the case? – Code_Ostrich May 08 '20 at 17:06
@Code_Ostrich Then it would be okay. – RobertS supports Monica Cellio May 08 '20 at 17:07
I tried with 0 but i am not getting the output. Only the first character is displaying. – Code_Ostrich May 08 '20 at 17:09
@Code_Ostrich What do you want to get as output instead? A string? Then use `%s` instead. – RobertS supports Monica Cellio May 08 '20 at 17:11
No i tried the same edited as i=0 and if condition as if(*(ptr+i) == ' ') { printf(" %c",*(ptr+i)); } – Code_Ostrich May 08 '20 at 17:12
@Code_Ostrich Yes, but what do you want to have as output? A string? – RobertS supports Monica Cellio May 08 '20 at 17:13
Now i am only getting the first character as o/p. I need the first character of the words in the string i entered. – Code_Ostrich May 08 '20 at 17:14
@Code_Ostrich What is your input? Any space before a word? – RobertS supports Monica Cellio May 08 '20 at 17:16
My input will be a word like computer science. I need the short form of this as 'C S'. – Code_Ostrich May 08 '20 at 17:17
@Code_Ostrich Then you need to use `printf(" %c",*(ptr+(i+1)));` because the offset points now to the white space instead of the first character of the second word. – RobertS supports Monica Cellio May 08 '20 at 17:22
@Code_Ostrich `printf(" %c",*(ptr+i));` -> `printf(" %c",*(ptr+(i+1)));` – RobertS supports Monica Cellio May 08 '20 at 17:23
Thanks a Lot friend. Thanks for helping a noob – Code_Ostrich May 08 '20 at 17:24
@Code_Ostrich It was a pleasure to help you. If this answer helped you with your problem, feel free to accept it. :-) – RobertS supports Monica Cellio May 08 '20 at 17:25
Sure dear friend. – Code_Ostrich May 08 '20 at 17:28

Display short form of a string

1 Answers1