Consider this example:

#include <stdio.h>

int main(void){
	//constant string (character pointer)
	const char *str = "Hello world";
	
	//changing first character
	str[0] ='p';  //will return error	
	printf("str: %s\n",str);
	
	return 0;
}

Output

main.c: In function 'main':
main.c:8:9: error: assignment of read-only location '*str'
  str[0] ='p';  //will return error 
         ^

Here, the statement str[0]='p' will try to change the first character of the string, thus, the "Error: assignment of read-only location" will occur.

How to fix?

Do not change the value of a constant during program execution.