How much faster is this: int run_switches(const char *buf) { size_t len = strlen(buf); int res = 0; for (size_t i = 0; i < len; ++i) {

How much faster is this: int run_switches(const char *buf) { size_t len = strlen(buf); int res = 0; for (size_t i = 0; i < len; ++i) { res += (buf[i] == 's') - (buf[i] == 'p'); } return res; } strlen() should be implemented in a pretty fast way, and after the buffer size is known, the compiler can autovectorize the inner loop, which does happen in practice: https://gcc.godbolt.org/z/qYfadPYoq https://gcc.godbolt.org/z/qYfadPYoq