c: 我不明白的东西

Question

I have this code :

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int i,j;
long int maxc=0,nn;

long int max(long int n)
{
    maxc=0;nn=n;i=1;

    if(n<10 && n>=0) 
        return n;

    while(nn!=0)
    {
        if(maxc<nn%10) 
        { 
            maxc=nn%10;
            j=i;
        }
        i++;
        nn/=10;
    }

    return maxc*(pow(10,i-2))+max(n/(pow(10,j))*(pow(10,j-1))+n%((int)pow(10,j-1)));
}

int main()
{
    long int n;
    printf("Dati n: ");
    scanf("%d",&n);
    printf("%ld",max(n));
    return 0;
}

n= numer given by user max=function that returns the maximum number consists of digits of n. EG: for n=1234.max should return 4321,for n=26341 ,max should return 64321

The problem is that sometimes works compiler,i mean for some number it returns the value I expect,but sometimes not. usually return the same number of digits ,but replace (a) digit/s with 9 or 4... I can't get a rule to fix this problem.

Thank you ! I used codeblocks for ubuntu.

Answer 1

Stay away from pow . It is a floating-point function that approximate the result. If it return a value slightly too small (say 2.9999 rather than 3.00000), your code will truncate it to the nearest lower value (2).

I would strongly suggest an integer or character solution.

Answer 2

I won't give you the entire solution, but i will give you the idea.

• Scan the digits from the keyboard and store them in a long int variable.
• Covert the digits to characters in an array. (don't forget about ASCII code).
• Sort he array in descending order.

• Print the array taking care of the ASCII code ( in my example i stored values not chars that's why i can print them as %d ).

   /* Prototypes*/ int stringConverter( char const * a, long int val ); void decsort( int * const a, int digits); int main( void ) { char a[ SIZE ]; int digits; long int val; printf( "Enter the number: " ); scanf( "%ld", &val ); digits = stringConverter( a, val ); decsort( a, digits ); /* Printer */ for( i = SIZE - digits - 1; i < SIZE; i++){ printf( "%d", a[ i ] ); } return 0; } int stringConverter( char * const a, long int val ) { int i, int j = 0; for( i = ( SIZE - 1 ); i >= 0; i-- ){ *( a + i ) = ( val % 10 ); j++; val = val / 10; if( val < 10 ){ i--; *( a + i ) = val; j++; break; } } return j; } void decsort( char * const a, int digits ){ /* Any sort */ }