fgets reads byherself data

First I apologize for taking so much space. So this is my problem...
I am writing this little programm for a mock exam and i am supposed to create functions for bitwise operations (smth like a veeeeeery simple binary calculator). Anyway I used the fgets function within a while loop. Right after I call another function which is basicly a loop, and as far as I have understood the fgets reads somth byhereself and goes ino an infite loop.Here is the code (I have deleted the parts not interested...)

Code:

 
#include <stdio.h>
#include <stdlib.h>
 #define bit_len 24 
  void decimal();
  void binary();

main()	
{
	
 int choice; 
 	printf("Will you use the binary(0) or the decimal(1) system: ");
 	scanf("%1d",&choice);
 	switch (choice)	{
    	case 0: binary();   break;     
        case 1: decimal();  break;
        default:  printf ("Min ise malakas, vale 1 i 0... ;-(\n\n");  break;
    }
		
 system("pause");
}

void binary()
{
	
 int i,check=0;	
 char operand1[bit_len],operand2[bit_len];
 char *ptr;
  
 	do	{
		printf("\n\nOperand No1(Up to 24 bits)\nRemember,only '0' and '1': ");
 		fgets(operand1,sizeof(operand1),stdin); 
		check=check_bin(operand1,check);
	}	while(check!=1);	
 	printf("%d",check);
 	
}

int check_bin(char *opr,int check)
{
 	while(*opr!='\0')	{
		check=(*opr=='0')||(*opr=='1')?1:0;
		if (check=0)		
			break;
	}
	return check;
}

void decimal()
{}

You can run it (It runs as itis) and see foryoureself.
If someone can help I would really appreciate it.

Originally Posted by Phoenix_Rebirth

Code:

int check_bin(char *opr,int check)
{
 	while(*opr!='\0')	{
		check=(*opr=='0')||(*opr=='1')?1:0;
		if (check=0)		
			break;
	}
	return check;
}

I'm not going to say much, as this is supposed to be teaching you something...

Your loop here never increments the pointer, so it always looks at the same character, so if it is valid (that is, a '0' or a '1'), you'll never exit the loop.

Hmmmm.... You are right. Actually I must have missed it in the hurry but the fact remains that for some reason the fgets reads something the first time and the program goes on and calls the function and therefore the loop. What I want to know is why it does that. I even tried fflush(stdout) in case of smth in the buffer but nothing. If i run it the
" printf("\n\nOperand No1(Up to 24 bits)\nRemember,only '0' and '1': "); "
command is executed twice meaning it has already done one loop.

That problem is due to you mixing scanf and fgets in the same program.
http://faq.cprogramming.com/cgi-bin/...&id=1043284385
http://faq.cprogramming.com/cgi-bin/...&id=1043284385
http://faq.cprogramming.com/cgi-bin/...&id=1043284392

Yes. You are right I completely forgot about that.... Thanks a lot

Code:

int check_bin(char *opr,int check)
{
 	while(*opr!='\0')	{
		check=(*opr=='0')||(*opr=='1')?1:0;
		if (check=0)
			break;
	}
	return check;
}

Your if(check=0) should be if(check==0). And why do you pass in check? It looks like it could be a local variable.