Explaining to someone why type casting isn't done automatically at compile time

Question

Recently, while I was writing a brief introduction to C for Fortran programmers, one of said Fortran programmers asked me about type casting. To him, it did not really make sense that in C you have to explicitly cast variables instead of having the compiler do it for you automatically.
I actually had a bit of hard time making my point that this is good thing because it helps in avoiding unintentional errors.

How would you justify this?

Answer 1

C does not need casts. Conversions are mostly done automatically at compile time.

This works and is idiomatic C

#include <stdio.h>
int main(void) {
    double x;
    int i;

    x = 42;                  /* automatically convert `int` to `double` */
    i = x;                   /* automatically convert `double` to `int` */
    printf("%f\n", i * 1.0); /* automatically convert `int` to `double` */

    printf("%d\n", (int)x);  /* explicit conversion needed */

    return 0;
}

Too many casts in a program indicate the programmer was (probably) using a C++ compiler to compile a C source file. Some (many??) uses of casts are just plain wrong.