Use name[strlen(name)] = d
.
char *name = malloc(80);
// some code that puts something in *name
strcpy(name, "Hello World");
char d = 'a'
size_t len = strlen(name);
if (len >= (80-1)) DealWithNotEnoughRoom();
name[len++] = d;
name[len] = '\0';
BTW:
char *name
is not a string literal. "Hello World" above is a string literal.
char *name
is a variable "name as pointer to char".