Thread: I need help with these 2 programs

I am new to C, literally. My lovely professor wants us to teach ourselves to program while he compiles it and tells us we're wrong without going into any details. If it compiles and it runs = A, if it doesn't = F. There's no inbetween. By the way, this is to be compiled using "gcc" in an UNIX environment

part a:
First of all, you are supposed to write a program in either C or C++ that reads data from a file and copies it to another file. Your program should copy all contents of the file.

part b:
Secondly, write another program to create child processes from your main program recursively using fork( ) and exec( ) commands up to a certain level, for example, fifth level. Then print identification of each child process in each level.


My code:

Part A:

Code:

#include<stdio.h>
#include <string.h>

int main(void)
{
	// open a text file for reading
	FILE *in_file
	in_file = fopen("input.txt","r");

	// open a text file for writing
	FILE *out_file
	out_file = fopen("input.txt","w");


	if(!f)
	{ return 1; }

	while(fgets(s,80,in_file) != NULL)
	{	
		//write to file
		fprintf(out_file, "%s",s");
		fprintf(out_file, "\n");
	}

	fclose(in_file);
	fclose(out_file);
	system("pause");
   	return 0;  
}

Part B:

Code:

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

int main()
{
   /* call the recursive function */
   recurse(5);
}


void recurse(int count)
{
   Pid_t pid;
   pid = fork(); 

   if(pid < 0)
   {
      /* if the fork failed give error */
      fprintf(stderr, "Fork Failed");
      exit(-1);
   }

   else if (pid == 0) 
   { 
      /* child process and print the ID*/
      execlp("/bin/ls", "ls", NULL);
      printf("Child Process ID: " + pid);
   }

   else 
   { 
      /* parent process */
      /* parent will wait for the child to complete */
      wait (NULL);
      exit(0);
   }


   /* if the count is less than one, we're finished */
   if(count > 1)
   { 
      exit(0); 
   }

   /* decrement count and call itself (recursion) */
   else
   {
      count = count - 1;
      recurse(count - 1)
   }
}

Please helpe me?!!?! What am I doing wrong? What am I missing? This guy told me it'd be easy because I "know" Java and it isn't. I honestly think learning Ada was a lot easier than C.

Woops, I meant to change the code to output.txt that's why.

Should it be something like this?

Code:

void main(void)
{
	FILE *fp; 
	int i;


	if ((fp = fopen("myfile", "w"))==NULL)
	{
		printf("Cannot open file \n");
		exit(1);
	}

	i=100;

	if (fwrite(&i, 2, 1, fp) !=1)
	{
		printf("Write error occurred");
		exit(1);
	}

	fclose(fp);


	if ((fp =fopen("myfile", "r"))==NULL)
	{
		printf("Read error occurred");
		exit(1);
	}

 	printf("i is %d",i);
 	fclose(fp);
}