#include "stdio.h"

void main(void)
{
  char *msgs[]={"123"};
  char *pc;
  
  pc=msgs[0];  
  pc[0]='0';

  printf("%c\n",pc[0]);
}

char *msgs[]={"123"}; // указатель на массив КОНСТАНТНЫХ строк

4.2 Array-to-pointer conversion
...

2 A string literal (2.13.4) that is not a wide string literal can be converted to an rvalue of type “pointer to char”;
...

2.13.4/1
A string literal is a sequence of characters (as defined in 2.13.2) surrounded by double quotes, optionally
beginning with the letter L, as in "..." or L"...". A string literal that does not begin with L is an ordinary
string literal, also referred to as a narrow string literal. An ordinary string literal has type “array of n
const char” and static storage duration (3.7), where n is the size of the string as defined below, and is
initialized with the given characters.
...

char * p = "ABC";

p[0] = 'D';

char * p = new char[4];
strcpy( p, "ABC\0" );
p[0]='D';

char m[] = "ABC";
char * p = m;
p[0] = 'D';

A>char * p = "ABC";
A>

int a1 = 5;
int a2 = a1 *= 2;

char *a = "aaa";
a[2] = b;
printf("aaa");

void foo()
{
char *s = "aaa";
printf("s=%s\n", s)
s[2] = b;
printf("s=%s\n", s)
}
...
foo();
foo();

char *s="123";

char bs[]="123";
char *s=bs;

char s[]="123";

А>>>char s[]="123";
А>>>

А>нет он получается если написать char *s="123";

char s[]="123";
s++;

W>>char s[]="123";
W>>s++;
W>>

char *s="123"; // указатель (но можно только читать)

char bs[]="123"; 
char *s=bs;      // указатель

char s[]="123";  // массив (т.к. s нельзя менять я назвал его константым указателем)