无法编译来自 The C Programming Language 的示例程序

Question

I know programming in Java, but I'm reading "The C Programming Language", second edition. It says that to compile and run a program from the command line you have to do:

$ cc hello.c  //assuming the name of the file is hello.c
./a.out

and hello world is printed. I tried that and worked fine.

---

Now, there is another example that prints a bunch of Celsius and Fahrenheit temperatures, so I created a file called TemperatureConverter.c with the given code. However, in the command line, when I ran:

$ cc TemperatureConverter.c

I got an error:

/usr/lib/gcc/x86_64-redhat-linux/4.8.3/../../../../lib64/crt1.o: In function `_start': (.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status

I don't know what this means. I tried double checking my syntax and it looks correct. I included the screenshot of the given code compared to the code I wrote, in case anybody notices a difference that may be causing the error:

#include <stdio.h>

main()
{
  float fahr, celcius;
  int lower, upper, step;

  lower = 0;
  upper = 300;
  step = 20;

  fahr = lower;
  while (fahr <= upper) {
    celcius = (5.0/9.0) * (fahr - 32.0);
    printf("%3.0f %6.1f\n", fahr, celcius);
    fahr = fahr + step;
  }
}

Answer 1

I just ran your code in cygwin using the same command and it compiled/ran fine. I will say the same things others have mentioned.

1. main has the return type int.
2. it's parameters should be (void) or (int argc, **int argv). You can have main() however this lets any parameters be passed into the main function.
3. Third the main function should end with return 0; This indicates that the program exited correctly.

In the end it should look like this

#include <stdio.h>

int main(void)
{
  float fahr, celcius;
  int lower, upper, step;

  lower = 0;
  upper = 300;
  step = 20;

  fahr = lower;
  while (fahr <= upper) {
    celcius = (5.0/9.0) * (fahr - 32.0);
    printf("%3.0f %6.1f\n", fahr, celcius);
    fahr = fahr + step;
  }
  return 0;
}

Answer 2

There's absolutely nothing syntacticly wrong with your code. Though the modifications suggested by FrozenHawk are a good idea. I noticed the linker error talks about an undefined reference to main in function _start . I've never even heard of a function _start as the starting point in ac file; though that could be an internal, compiler specific, thing not strictly specified in the standards.

You should be absolutely sure you're trying to compile the correct file. Use cat on the same argument for extra assurance. Your code compiled just fine for me, as is, and with the commands you used on Debian. It seems unlikely, but this could be an issue with gcc. On my machine, no function called _start appears in any files in /usr/include/ , which implies something lower level. You might consider uninstalling and reinstalling as a last resort.