How do you check if a c code is comiling with linux?

Question

I submitted a C Code for an homework I had and for me and my friends. It seemed to be working with no warnings. We used VSCodium and a Terminal with an texteditor and a Debug Console, to both it seemed to be working just fine.

My teacher still said, that it didnt compile and that's why we got 0 points for it. I would like to ask if there are any other options to test if a code is working (a website, or to download something extra etc). I use the Linux system.

If someone has a tip I would really appreciate it. (If someone could check thess two codes for warnings/or if its compiling for me, would be nice)

the first is a calc.c

#include<stdio.h>

int main(){
char operator;
double num1, num2;

printf("Geben sie einen Operator ein (+, -, *, /): ");
scanf("%c", &operator);

printf("Geben sie die beiden Zahlen nacheinander ein: ");
scanf("%lf %lf", &num1,&num2);

switch (operator)
{

case '+':
   printf("%.2lf + %.2lf = %.2lf",num1,num2,(num1+num2));
   break;

case '-':
   printf("%.2lf - %.2lf = %.2lf",num1,num2,(num1-num2));
   break;

case '*':
   printf("%.2lf * %.2lf = %.2lf",num1,num2,(num1*num2));
   break;

case '/':
    if( num2 != 0.0 )
        printf("%.2lf / %.2lf = %.2lf", num1,num2,(num1/num2));
    else 
        printf("durch 0 teilen geht nit");
    break;


default:
    printf("%c ist kein gültiger Operator",operator);
    break;
}

return 0;

}

and the second cat.c

#include<unistd.h>
#include<stdio.h>
#include<fcntl.h>

int main()
{
    int fd;
    char buf[80];
    char msg[50] = "hallo, hier steht immer was in foo steht";
    fd = open ("foo.txt", O_RDWR);
    printf("fd = %d", fd);
    if (fd != -1)
{
    printf("\n foo.txt wurde mit (sys)read und (sys)write geoffnet\n");
    write(fd, msg , sizeof(msg));
    lseek(fd,0,SEEK_SET);
    read(fd, buf, sizeof(msg));
    printf("\n %s wurde in die datei geschrieben\n", buf);
    close (fd);
}

return 0;
}

this one should read what is written in foo.txt and other textdatas by calling it with e.g. "cat foo.txt bar.txt baz.txt"

Answer 1

There's nothing wrong with the programs.

I think your professor is compiling with g++. operator is a keyword in C++

I tried compiling with g++ and I got these warnings:

calc.c: In function ‘int main()’:
calc.c:4:14: error: expected type-specifier before ‘;’ token
    4 | char operator;
      |              ^
calc.c:8:22: error: expected type-specifier before ‘)’ token
    8 | scanf("%c", &operator);
      |                      ^
calc.c:13:17: error: expected type-specifier before ‘)’ token
   13 | switch (operator)
      |                 ^
calc.c:37:53: error: expected type-specifier before ‘)’ token
   37 |     printf("%c ist kein gültiger Operator",operator);
      |                                                     ^
make: *** [Makefile:7: calc] Error 1

Maybe provide your professor with a Makefile?