Parameters and Return Values

Parameters are copies

void set_to_zero(int x) {
    x = 0;                    // modifies the COPY — caller unaffected
}

int a = 5;
set_to_zero(a);              // a is still 5

C passes by value, always. The function's parameter is a fresh variable initialized with the argument's value. (Output parameters via pointers come in module 11 — this is the "why".)

One return value

int clamp(int v, int lo, int hi) {
    if (v < lo) return lo;
    if (v > hi) return hi;
    return v;
}

return exits immediately — it can appear anywhere in the body. A non-void function that reaches the end of its body without a return hands the caller an indeterminate value (undefined behavior if the caller uses it). GCC warns with -Wreturn-type; our harness compiles with warnings shown.

Early returns beat nesting

// prefer this                          // over this
int f(int x) {                          int f(int x) {
    if (bad(x)) return -1;                  if (!bad(x)) {
    ... main path ...                           ... deep nesting ...
}                                           }
                                        }