star pattern using recursive func in c-CodePudding

I am trying to develop a C code that generates * a pattern by given input. First it must print star descending by 2 and after ascending by 2. like:

input

enter number: 8

output

********
******
****
**
****
******
********

here is what i did so far:

#include <stdio.h>

int printpattern(int n){
    if(n==0)return 0;
    printf("*");
    printpattern(n-1);
}

int pattern(int n){
    if(n==0)return 0;
    puts("\n");
    printpattern(n);
    pattern(n-2);
}

int main(){
    int n;
    puts("number: ");
    scanf("%d", &n);
    if(n%2==1){
        puts("must be even");
        main();
    }
    pattern(n);
    return 0;
}

thanks..

CodePudding user response：

Calling the function main recursively will result in executing these statements in each invocation of main

puts("number: ");
scanf("%d", &n);

So it is not a good idea to call main recursively.

I would write the function the following way as it is shown in the demonstration program below.

#include <stdio.h>

void print_pattern( unsigned int n )
{
    if ( n )
    {
        putchar( '*' );
        print_pattern( n - 1 );
    }
}

void pattern( unsigned int n )
{
    if ( n )
    {
        print_pattern( n );
        putchar( '\n' );
        
        if ( n > 2 )
        {
            pattern( n - 2 );
            print_pattern( n );
            putchar( '\n' );
        }
    }
}
    
int main(void) 
{
    while ( 1 )
    {
        printf( "Enter a non-negative number (0 - exit): " );
        
        unsigned int n;
        
        if ( scanf( "%u", &n ) != 1 || n == 0 ) break;
        
        putchar( '\n' );
        
        pattern( n );
        
        putchar( '\n' );
    }
    
    return 0;
}

The program output might look like

Enter a non-negative number (0 - exit): 8

********
******
****
**
****
******
********

Enter a non-negative number (0 - exit): 7

*******
*****
***
*
***
*****
*******

Enter a non-negative number (0 - exit): 6

******
****
**
****
******

Enter a non-negative number (0 - exit): 5

*****
***
*
***
*****

Enter a non-negative number (0 - exit): 4

****
**
****

Enter a non-negative number (0 - exit): 3

***
*
***

Enter a non-negative number (0 - exit): 2

**

Enter a non-negative number (0 - exit): 1

*

Enter a non-negative number (0 - exit): 0

Of course you can call the function only for even numbers though the function is more general and can be called for any non-negative number.

The function itself should not depend on whether an even or odd number was passed to it.

CodePudding user response：

I think if the question states you must use recursion, it makes a lot more sense to use recursion this way:

#include <stdio.h>

static void printstars(int n)
{
    for (int i = 0; i < n; i  ) {
        printf("*");
    }
    printf("\n");
}

static void printpattern(int n)
{
    printstars(n);
    if (n > 4) {
        printpattern(n - 2);
    } else {
        printstars(2);
    }
    printstars(n);
}

int main(void)
{
    int n;
    puts("number: ");
    scanf("%d", &n);
    if (n & 1) {
        fprintf(stderr, "must be even\n");
        return 1;
    }
    printpattern(n);
    return 0;
}