C编译器未注意到错误并更正代码本身

Question

所以我是C语言的初学者，我一直在关注Primer Plus 6th Edition。在运行程序时，我发现确实有些奇怪，例如，编译器无法正常工作。

int main(){
    one_three();
    getchar();
    return 0;
}

void one_three(void){
    printf("one\n");
    two();
    printf("three");
}

void two(void){
    printf("two\n");

}


这是我的代码，因为没有函数原型声明并且不包括头文件，所以有很多错误，但是有些输出仅通过发出警告来产生，我不认为这应该发生]]
输出为：

review1.c: In function 'main':
review1.c:2:5: warning: implicit declaration of function 'one_three' [-Wimplicit-function-declaration]
    2 |     one_three();
      |     ^~~~~~~~~
review1.c:3:5: warning: implicit declaration of function 'getchar' [-Wimplicit-function-declaration]
    3 |     getchar();
      |     ^~~~~~~
review1.c:1:1: note: 'getchar' is defined in header '<stdio.h>'; did you forget to '#include <stdio.h>'?
  +++ |+#include <stdio.h>
    1 | int main(){
review1.c: At top level:
review1.c:7:6: warning: conflicting types for 'one_three'
    7 | void one_three(void){
      |      ^~~~~~~~~
review1.c:2:5: note: previous implicit declaration of 'one_three' was here
    2 |     one_three();
      |     ^~~~~~~~~
review1.c: In function 'one_three':
review1.c:8:5: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    8 |     printf("one\n");
      |     ^~~~~~
review1.c:8:5: warning: incompatible implicit declaration of built-in function 'printf'
review1.c:8:5: note: include '<stdio.h>' or provide a declaration of 'printf'
review1.c:9:5: warning: implicit declaration of function 'two' [-Wimplicit-function-declaration]
    9 |     two();
      |     ^~~
review1.c: At top level:
review1.c:13:6: warning: conflicting types for 'two'
   13 | void two(void){
      |      ^~~
review1.c:9:5: note: previous implicit declaration of 'two' was here
    9 |     two();
      |     ^~~
review1.c: In function 'two':
review1.c:14:5: warning: incompatible implicit declaration of built-in function 'printf'
   14 |     printf("two\n");
      |     ^~~~~~
review1.c:14:5: note: include '<stdio.h>' or provide a declaration of 'printf'
one 
two
three

那些最后三行“一”二三是输出请帮助，我正在使用此编译器

我希望它在需要时会输出错误，并且本身不会添加任何东西，这样我就可以从我的错误中学到使用带有扩展名的Visual Studio代码：Microsoft的C / C ++，代码运行器

所以我是C语言的初学者，我一直在关注Primer Plus 6th Edition。在运行程序时，我发现确实有些奇怪，编译器无法正常运行，因为...

Answer 1

您在顶部缺少函数原型：

void two(void);
void one_three(void);

int main(){
    one_three();
    getchar();
    return 0;
}

void one_three(void){
    printf("one\n");
    two();
    printf("three");
}

void two(void){
    printf("two\n");

}

Answer 2

您需要在使用它们的函数上方声明要在函数中使用的方法。如果将这些函数重新排序为2，则将one_three排序为main。应该可以。