Printing all binary strings of length N using recursion (in c)

Question

I need to print all binary string of length N counting from 0 to the highest number that can represented. My code below works for generating all of the strings. The problem I am having is that the strings are not in order from least to greatest.

#define MAX_LENGTH 10

char binarystrings[MAX_LENGTH];

void binary(int n) {
    if (n == 0) {
        printf("%s\n", binarystrings);
    } else {
        binarystrings[n-1] = '0';
        binary(n-1);
        binarystrings[n-1] = '1';
        binary(n-1);
    }
}

int main() {
    int length;
    scanf("%d", &length);
    binary(length);
}

When my program takes in 3 it generates:

But I need it to generate:

How should I go about making my program put the numbers out in the right order?

Did you notice that the reverse of each line is in the order you want? — pmg
– pmg, Commented Feb 23, 2019 at 18:43
Yes, I did. I could've used used string reverse but it wouldn't have helped me to see why they were out of order. I now see that I was filling the array backwards so now I can avoid string reverse entirely. — arctic
– arctic, Commented Feb 23, 2019 at 19:20

user58697 · Accepted Answer · 2019-02-23 18:20:31Z

1

You are filling the binarystring right to left. Fill it left to right instead. For that you need to pass two parameters (e.g. position and length) to binary:

void binary(int index, int length)
{
    if (index == length)
        return;
    binarystring[index] = 0;
    binary(index + 1, length);
    binarystring[index] = 1;
    binary(index + 1, length);
}

and call it as binary(0, length).

answered Feb 23, 2019 at 18:20

user58697

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Comments

newbie · Accepted Answer · 2019-02-23 17:51:03Z

0

what about printf("%s\n", strrev(binarystrings)); It would probably be safer to reverse the string and check for error then print it and initializing your char array to contain nulls..and finally doesn't the array need to be MAX_LENGTH +1

answered Feb 23, 2019 at 17:51

newbie

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Comments

kamli_kamli · Accepted Answer · 2021-07-13 04:55:14Z

0

u can try my code ... i have got the answer in the right pattern:

enter code here

#include <stdio.h>
void printBinary(int a[],int n){
    
    for (int i=0;i<n;i++){
        printf("%d",a[i]);
    }
    printf("\n");
    
}

void generateBinaryString(int n,int a[],int i){
    
    if (i==n){
        printBinary(a,n);
        return;
    }
    
    a[i]=0;
    generateBinaryString(n,a,i+1);
    a[i]=1;
    generateBinaryString(n,a,i+1);
}

int main()
{
    int n;
    printf("printing the binary string for n nos.");
    scanf("%d",&n);
    int a[n];
    
    generateBinaryString(n,a,0);

    return 0;
}

answered Jul 13, 2021 at 4:55

kamli_kamli

1

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