C program increment letters in a string

Question

I'm learning C, and I encountered a problem when I tried to increment letters in a string. Consider the code below:

int main() {
    char *s = "abcdefg";
    increment(s);
    printf("%s\n", s);
} 

void increment(char *string) {
    for (int i = 0; string[i] != 0; i++) {
        (*(string + i))++;
    }
}

Currently I'm using C99. After I tried executing this, it gives be Bus Error: 10. I don't know why this is the case. Thanks!