Decimal to binary C while dividing by 2 - c

Question

I have to write 2 programs that convert dec to bin. I've finish the 1st one however when I try to run this one it prints out an array of random number not sure why, here is what I have:
#include <stdio.h>
int getNumber();
int dectoBin(int, int binarray[], int);
void printBin(int binary[], int dec);
int main()
{
int M = 8;
int binarray[M];
int dec = getNumber();
printf("The decimal number you entered was: %d", dec);
decToBin(dec, binarray, M);
printBin(binarray, dec);
return 0;
}
int getNumber()
{
int dec;
printf("Enter any a number between 0 and 255: ");
scanf("%d",&dec);
return dec;
}
int decToBin(int dec, int binarray[], int M)
{
int i, j;
for(i=8; i>=0;i--)
{
while(dec != 0)
{
binarray[i]= dec % 2;
dec = dec / 2; binarray[i] = dec;
}
}
return *binarray;
}
void printBin(int binary[], int dec)
{
int i;
if(dec > 255)
{
printf("please use another number");
main();
}
else
{
for(i =8; i >= 0;i--)
{
printf("%d", binary[i]);
printf("\n");
}
}
}

Answer 1

You're setting binarray[i] twice - once correctly (after the modulus statement) and once incorrectly (after dividing dec). So if your decimal number is 65, your second-to-last number would be 32.
You can also make binarray an array of bits rather than numbers. This would have given you a error on compilation and would have perhaps clued you into the logical error.
EDIT: There are a lot of control flow issues with this program. You should check to see if dec > 255 BEFORE calling decToBin otherwise the program will run incorrectly. decToBinary shouldn't return an int - it should return an array of ints (or bits as I suggested) and that is what you should send to printBin. Right now you're returning the pointer to binArray (do you know what pointers are?) decToBin should also return void since it does not perform any calculations.
EDIT 2: As someone else pointed out your array indexes are incorrect, I don't know how you haven't gotten an array out of bounds error. Also, while printing you're going the wrong way: You need to use a for loop that starts at 0 and ends at 7.

Answer 2

Here are some suggestions.
You have dectoBin in the declaration but decToBin in the function call and function definition. Make sure they are all dectoBin or they are all decToBin.
M is not used in decToBin. Feel free to remove it.
I would change getNumber() such that it checks for the range and makes sure that you get a number between 0 to 255 from its return statement. That would eliminate the need to do that check in printBin.
Implementation of decToBin is quite a bit simpler than what you were thinking. The for-loop can be simplified to:
for(i=7; i>=0;i--, dec /= 2)
{
binarray[i]= dec % 2;
}
And finally, implementation of printBin can be a little bit different to make the output more readable. Instead of printing one number at a time, they can all be printed in one line.
Here's what I came up with:
#include <stdio.h>
int getNumber();
int decToBin(int, int binarray[]);
void printBin(int binary[], int dec);
int main()
{
int M = 8;
int binarray[M];
int dec = getNumber();
printf("The decimal number you entered was: %d\n", dec);
decToBin(dec, binarray);
printBin(binarray, dec);
return 0;
}
int getNumber()
{
int dec;
printf("Enter a number between 0 and 255: ");
scanf("%d",&dec);
if( dec < 0 || dec > 255)
{
printf("Please use another number\n");
return getNumber();
}
return dec;
}
int decToBin(int dec, int binarray[])
{
int i;
for(i=7; i>=0;i--, dec /= 2)
{
binarray[i]= dec % 2;
}
return *binarray;
}
void printBin(int binary[], int dec)
{
int i;
printf("The decimal number in binary: ");
for(i=0; i!=8; ++i)
{
printf("%d", binary[i]);
}
printf("\n");
}
A sample execution and output:
~>>./test-07
Enter a number between 0 and 255: 149
The decimal number you entered was: 149
The decimal number in binary: 10010101