17 printf("element %zu is %g, \tits square is %g\n",
18 i,
19 A[i],
20 A[i]*A[i]);
!@%STYLE%@!
{"css":"{\"css\": \"font-weight: bold;\"}","target":"[[{\"line\":0,\"ch\":0},{\"line\":0,\"ch\":2}],[{\"line\":0,\"ch\":6},{\"line\":0,\"ch\":12}],[{\"line\":1,\"ch\":0},{\"line\":1,\"ch\":2}],[{\"line\":2,\"ch\":0},{\"line\":2,\"ch\":2}],[{\"line\":3,\"ch\":0},{\"line\":3,\"ch\":2}]]"}
!@%STYLE%@!
This call prints an array element and its square. Read it from the outside in: `printf` names the function; the parentheses contain four comma-separated arguments; the semicolon ends the statement. section 1.1
A function call hands control from the current function to the called function. Its arguments supply values for that invocation. In the example, the string literal specifies the output format, while `i`, `A[i]`, and `A[i]*A[i]` supply values for its three numeric positions. When the called function returns, execution continues after the call. section 1.1 section 2.4.2 section 17.4
TAKEAWAY: C passes argument values, not the caller’s variables. Passing `i` to `printf` does not let `printf` change `i` itself. Passing an address through a pointer is a separate way to give another function access to an object. section 2.4.2
extern double fbar(double);
...
double fbar2 = fbar(2)/2;
!@%STYLE%@!
{"css":"{\"css\": \"font-weight: bold;\"}","target":"[[{\"line\":0,\"ch\":3},{\"line\":0,\"ch\":16}],[{\"line\":0,\"ch\":10},{\"line\":0,\"ch\":16}],[{\"line\":3,\"ch\":3},{\"line\":3,\"ch\":9}],[{\"line\":0,\"ch\":10},{\"line\":0,\"ch\":16}],[{\"line\":3,\"ch\":3},{\"line\":3,\"ch\":9}]]"}
!@%STYLE%@!
The prototype says `fbar` expects a `double` and returns a `double`. In `fbar(2)/2`, the known parameter type lets the caller convert the integer argument to `2.0` before the call; the return type informs the surrounding expression. section 7.1
Parentheses have different jobs in a call and a declaration: a call contains arguments for one invocation; a prototype declares parameter types and a return type. Use `void` in the parameter list to declare a function called with no arguments, or as the return type when it returns no value. Each call has its own local objects, including when a function calls itself recursively. section 7.1 section 17.4
TAKEAWAY: The call operator `(...)` also applies to function pointers. Even an ordinary-looking call through a function name involves conversion to a function pointer in C’s abstract state machine. A function pointer can therefore select which function a call invokes. section 11.4
