Here I have a little C-51 program that I wrote as a puzzle using the Keil tools. I thought to post this because there have been a number of requests recently regarding learning C coding. What better way to sharpen C skills than to study some code. When you set out to evaluate this feel free to select a 3-digit decimal (base 10) number to assign to the you_pick variable. I would ask some questions about the program:

- First...What does this code actually produce?

- Second..What happens with different you_pick values.

- Third...Are all values for you_pick doing what you expect?

- Fourth...Why does this produce the behavior that it does?

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

unsigned int you_pick=123;              // select a 3 digit number

void main(void)
{
    int a=321, b, c;
    unsigned char str[11];
    unsigned char z;

    sprintf(str,"%03i %03i", b=you_pick, a);
    str[8]  =  str[4];
    str[4]  =  str[0];
    str[9]  =  str[5];
    str[5]  =  str[2];
    str[10] =  str[6];
    str[0]  =  str[2];
    str[5] -=  str[0];
    str[2]  =  str[4];
    str[3]  =  str[5];
    a = atoi(str);

    z = a > b;

    b = (z * a + !z * b) - (z * b + !z * a);

    sprintf(str, "%03i%03i", a=b, b);
    
    str[0]  = str[5];
    str[11] = str[6];
    str[2]  = str[3];
    str[3] -= str[2];
    str[7]  = str[9];

    sscanf(str,"%03i", &c);

    a = b + c + atoi(str+7)*3;

    sprintf(str,"%04d.com", a);

    while(1);
}

Have Fun !!
Michael Karas