Why does using the wrong format specifier in C crash my program on Windows 7?
You have wrong format specifier. %s is used for strings but you are passing size_t (strlen(string)). Using incorrect format specifier in printf() invokes undefined behaviour. Use %zu instead because the return type of strlen() is size_t.
So change
printf("That string is %s characters long.\r\n", strlen(string));to:
printf("That string is %zu characters long.\r\n", strlen(string));Since you are using gcc have a look here for more info what can be passed to printf