Convert to base in C

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Hello,

I'm new in the field. Unfortunately I don't understand the third function in this program I want to know what do

for(--digit; digit >= 0; --digit )

and

baseDigits[nextDigit]

.

Thank you.

What I have tried:

#include <stdio.h>
int convertedNumber[64];
long int numberToConvert;
int base;
int digit = 0;
void getNumberAndBase (void)

{
        printf ("Number to be converted? ");
        scanf ("%li", &numberToConvert); printf ("Base? "); scanf ("%i", &base);
        if ( base < 2 || base > 16 ) {
          printf ("Bad base - must be between 2 and 16\n"); base = 10; }
}
void convertNumber (void) {
        do { convertedNumber[digit] = numberToConvert % base;
             ++digit;
             numberToConvert /= base;
           }
              while ( numberToConvert != 0 );


}
void displayConvertedNumber (void) {
        const char baseDigits[16] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
        int nextDigit;
        printf ("Converted number = ");
        for (--digit; digit >= 0; --digit )
        {
          nextDigit = convertedNumber[digit];


          printf ("%c", baseDigits[nextDigit]);
        }
        printf ("\n");

}
int main (void) {
        void getNumberAndBase (void), convertNumber (void), displayConvertedNumber (void);
        getNumberAndBase ();
        convertNumber ();
        displayConvertedNumber ();
        return 0;
}

Posted 13-Apr-18 16:05pm

steve NN

Updated 13-Apr-18 19:51pm

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OriginalGriff · Accepted Answer · 2018-04-13T19:52:00

A for statement has four parts:

C#

for (a ; b ; c )
   d;

Where:
a is executed before the loop starts
c is executed after the loop has run
b is tested after c has executed
d is executed each time the loop runs.
In pseudo code it looks like this:

1) Execute a
2) If ( not b ) goto (3)
2.1) Execute d
2.2) Execute c
2.3) Goto (2)
3) done.

So in your case:

1) Subtract one from digit
2) if ( digit < 0 ) exit the loop.
2.1) Execute these lines:

nextDigit = convertedNumber[digit];
printf ("%c", baseDigits[nextDigit]);

2.2) Subtract one from digit
2.3) Loop round to (2) and check again.

The other code fragment is simple: baseDigits is an array, and your code

baseDigits[nextDigit]

extracts the element at the position given by the index value in nextDigit - so if the index is zero, it fetches the first character '0', if it's one it fetches '1', and so on up to fourteen 'E' and fifteen 'F'

You wrote this code for your homework, so you should really understand what it does...