#include <stdio.h>

void print_int(int x) { printf("int: %d\\n", x); }
void print_dbl(double x) { printf("double: %g\\n", x); }
void print_default() { puts("unknown argument"); }

#define print(X) _Generic((X), \\
        int: print_int, \\
        double: print_dbl, \\
        default: print_default)(X)

int main(void) {
    print(42);
    print(3.14);
    print("hello, world");
}

Output:

int: 42
double: 3.14
unknown argument

Note that if the type is neither int nor double, a warning would be generated. To eliminate the warning, you can add that type to the print(X) macro.