有人可以帮我解决 C 问题吗？ 当我尝试运行它不返回任何东西

Question

#include <stdio.h>
#include <stdlib.h>

double cube(double num) {
    return num * num * num;
}


int main(){

    Answer(cube(3.0));

    return 0;
}

void Answer(double cube()) {

    printf("Answer: %.1f\n", cube());

}

If you try to run it, doesn't work, at least on my computer. I tried to change some things like adding some more parentheses, but I can't find the solution.

Answer 1

I don't think your code compiles. Here's some quick fixes:

#include <stdio.h>
#include <stdlib.h>

void Answer(double); // forward declaration, you could also define Answer before main

double cube(double num) {
    return num * num * num;
}


int main(){

    Answer(cube(3.0));

    return 0;
}

void Answer(double value) {

    printf("Answer: %.1f\n", value);

}

Answer 2

Or simpler, move the Answer() function above main() below cube() .

C files are compiled in a Single-Pass . This means that before a function can be used, the compiler must know about it. (it has to already know what it is before it reaches the point where it is used)

With Answer() below main() (and no forward declaration), when the compiler reaches main() and sees Answer() it has no idea what it is yet. So one fix is to provide a prototype , a forward-declaration, promising the compiler that yes, this function will be defined later in the source file (or elsewhere).

Your other option (recommended for short functions) is to simply order the definition for the function in an order so each is defined before it is used. This will naturally end up with all functions defined above main() , but there is nothing wrong with that.

As the size and number of the functions you are using grows -- then it can be beneficial (convenient) to provide forward-declarations to help organize the code in a logical way that it can be split between a source and header file with minimal effort. In large source files organizing the forward declarations up top in the order they appear below main() also provides road-map to where the functions are defined (which may help you navigate to where you need to go, or provide a quick copy/paste into the search dialog)

@selbie has already provide your answer for using a prototype or forward-declaration. A simple reordering would be:

#include <stdio.h>

double cube (double num)
{
    return num * num * num;
}

void Answer (double value)
{
    printf ("Answer: %.1f\n", value);
}

int main (void) {

    Answer (cube (3.0));

    return 0;
}

( note: avoid including unneeded header files in your code)

How you want to handle it is completely up to you, but these are the normal considerations that go into your decision.