C segmentation fault xor char array - c

Question

I want to xor a certain value on all of my chars in a char array. I have some code that works all fine except for the xor line:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
void obfuscate(FILE *file, char *input, char *variableName)
{
int i;
int size = (int)strlen(input);
char a = 65;
fprintf(file, "%s: %s -> ", variableName, input);
for(i = 0; i < size; i++)
{
input[i] = (char)(input[i] ^ a);//I am causing a segmentation fault
fprintf(file, "0x%x, ", input[i]);
}
return;
}
int main()
{
char *a = "MyString";
FILE *file = fopen("out.txt", "w");
obfuscate(file, a, "a");
fclose(file);
}
I use the normal gcc compiler with gcc in.c -o out.o on a linux machine.
If I comment the line with the xor operation it works just fine. Any help is highly appreciated, my own research did not result in a solution.

Answer 1

Try below solution with dynamic memory.
In char *a = "MyString"; char *in = malloc(sizeof(a));
a is pointing to code section we can't alter it. &
in is pointing to heap section, so we can modify it any no.of times.
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
void obfuscate(FILE *file, char *input, char *variableName)
{
int i;
int size = (int)strlen(input);
char a = 65;
fprintf(file, "%s: %s -> ", variableName, input);
for(i = 0; i < size; i++)
{
input[i] = (char)(input[i] ^ a);//I am causing a segmentation fault
fprintf(file, "0x%x, ", input[i]);
}
return;
}
int main()
{
char *a = "MyString";
char *in = malloc(sizeof(a));
strcpy(in, a);
FILE *file = fopen("out.txt", "w");
obfuscate(file, in, "a");
fclose(file);
free(in);
}