Answer:
To guarantee that the value printed by main.c is 256, the variable n in foo.c must be initialized to 256 before it is used in the foo() function. This can be done by adding an initializer to the n variable, as shown below:
// foo.c
float n = 256;
void foo() {
n = n * 2;
printf("n = %f\\", n);
}
With this change, the n variable will be initialized to 256 when it is declared, and the value of n will be guaranteed to be 256 when it is printed by the foo() function. This will ensure that the value printed by main.c is always 256, regardless of the order in which the main() and foo() functions are executed.