What happens when we convert string literal to integer in C?

Question

Consider a C program:

#include <stdio.h>

int main (void)
{
  int x = 'a';
  printf("%d", x);
}

Here the output is 97 as per the ASCII value table.

But in the example below:

#include <stdio.h>

int main(void)
{
  int x ='aa';
  printf("%d", x);
}

The output is 24929.

Can anyone please explain how the literal has been converted to this integer value?

Your second example do not compile correctly: c is not defined, the x initialization is not correct. I think you've got an undefined behaviour. — Mathieu, Apr 05 '16 at 08:00
There are no string literals in your code, just character literals. — Spikatrix, Apr 05 '16 at 08:02
Note: The value of multicharacter literals is implementation defined. — Spikatrix, Apr 05 '16 at 08:03
And next time onwards, please post compilable code. I've edited it for you this time. — Spikatrix, Apr 05 '16 at 08:06
@purplepsycho the second example is *implementation-defined* and it should compile correctly — M.M, Apr 05 '16 at 08:11
Those are **not** string literals http://en.cppreference.com/w/c/language/string_literal but rather character literals http://en.cppreference.com/w/c/language/character_constant — CiaPan, Apr 05 '16 at 08:15
Relace `printf("%d", x);` by `printf("%x", x);` and it will be clearer. — Jabberwocky, Apr 05 '16 at 08:20
@MichaelWalz: not really – a better test would be with two *different* characters. — Jongware, Apr 05 '16 at 08:26

Giorgi Moniava · Answer 1 · 2016-04-05T08:17:41.383

3

int x ='aa';

This is valid but value of x is implementation defined. And btw, this is not a string literal. String literal would be this "aa".

edited Apr 05 '16 at 08:17

answered Apr 05 '16 at 08:09

Giorgi Moniava

What do we call it then, actually I could'nt find the name so I wrote string literal. – smartnerd Apr 05 '16 at 10:34
@smartnerd Probably multicharacter constant – Giorgi Moniava Apr 05 '16 at 11:51

Boiethios · Answer 2 · 2016-04-05T08:18:01.687

0

You assigned a value to the int using octets : 'a' is 0x61.

So writing int x = 'aa' is like writing int x = 0x6161.

Edit: but do not write that. Just write int x = 0x6161 or int x = 24929.

edited Apr 05 '16 at 08:18

answered Apr 05 '16 at 08:07

Boiethios

2 Answers2