How to make constant string

Source Code
#include <stdio.h>

#define PI 3.14 // proprocessor
#define TRUE 1
#define FALSE 0
#define STRING_HELLO "hello hello"

int main() 
{
const double pi=3.14; // double type guarantee 14 digits of the decimal point
const int tru=1;
const char *string_hello="hello hello2";

printf("#define :: PI=%f, string=%s\n",PI,STRING_HELLO);
printf("#define :: pi=%f, string=%s\n",pi,string_hello);
if(tru)
{
printf("true\n");
}
}