Thread: Manipulating a large, random string

I can't quite wrap my head around a good approach to to randomly printing a word (as a string of characters) into an already printed box of random letters. I figure this would all be done to a file, but considering I'm an amateur at file manipulation, this is difficult.

I can construct the box of letters:

Code:

void bld(char str[11]){
int i, j, rng;
char alpha[27] = "abcdefghijklmnopqrstuvwxyz";

FILE *fp;

fp = fopen("foo.txt", "w")

for (i=0; i < VER; i++){
        for (j=0; j < HOR; j++){
            rng = rand() % 26;
            fprintf(fp, "%c", alpha[rng]);
        }
        fprintf(fp, "\n");
    }
 
fclose(fp);

return;
}

From here, I'm at a mental road block.

Does anyone know any good methods for modifying the printed string?