Question

Gurus,

I want to know how to write a recursive function that prints

1
12
123
1234
…
……

For eg: display(4) should print

1
12
123
1234

Code

#include <stdio.h>

void print(int n)
{
        if(n != 0)
        {
                print(n-1);
                printf("\n");
                print(n-1);
                printf("%d",n);
        }
}
int main()
{
        print(3);
}

Output

1

12

1

123

Issues

I wanted to write a pure recursive (without any loop) function but unable to filter unwanted prints.
Hope someone will help me out!!!

Update

Thanks all for the answers.From all the comments which were given it seems like we can write one with only recursion and a loop is required.

Answer 1

To define a recursive function, you have to do three things:

1. Define what the function does. In this case it is printing numbers from 1 up to n.
2. Define what the recursive call is. What happens the next time around? The easiest way is to think from the bottom up; in this case, on each earlier line, it is printing numbers up to one less than the previous. Therefore, every time you call the function again, you want to call it with one less than the previous number.
3. Define your stop condition. When should I stop recursing? In this case, once you hit the number 1, this will be your last iteration. This means, we want to call the recursive function until this stop condition is reached – or in other words, while n is greater than 1.

Therefore, we end up with the following algorithm:

function display(n):
    if(n > 1):
        display(n-1);

    print 1..n;