Can someone help me understand this example program
This is a sample program that my tutor gave me. However, I have very much trouble understanding the second if statement. Would somebody plz be able to explain it to me, in not too difficult language :(
Code:
#include <stdio.h> //Handles the keyboard input and screen output
#include <process.h> //Handles DOS system commands ("cls", "pause", etc.)
#include <conio.h> //Handles: getch(), getche().
#include <string.h> //Handles string functions.
int main(void)
{
//This part declares variables used by the entire program
int Arabic=0; //Integer declaration to store Arabic number
char Roman[30]; //String declaration to store a Roman number
//This part declares variables used and reads Arabic numbers
int counter = 7; //Declares the count of digits in Roman numbers
char T_Roman [7] = "MDCLXVI"; //Lists all digits of Roman numbers
int T_Arabic [7] = {1000, 500, 100, 50, 10, 5, 1};//Values of Roman digits
int length=0; //Stores the length of an input Roman number
int in, list; //Declare operational loop counters
int last_in, last_list;//Store the previous digits being considered
textcolor(6); //This defines color of the writing for "cprintf"
cprintf("This program converts Roman numbers into Arabic numbers.");//Colour
//This part reads Raman numbers with "scanf" and "printf"
printf("\nType a valid Roman number (e.g. MCMXCIX) up to 30 chars long: ");
scanf("%s", Roman); //Inputs a Roman number
length = strlen(Roman);
strupr(Roman);
printf("The Roman number |%s| is %d characters long.", Roman, length);
fflush(stdin); //flushes the input buffer
//This part contains the algorithm of converting Roman numbers into Arabic:
in=0;
last_in = length + 1;
last_list = length + 1;
while (in < length) //Loop along the chars of the Roman number
{
for(list=0; list < counter; ++list) //Loop along the Roman symbols
{
if (Roman[in] == T_Roman[list])
{
/*printf ("\nRoman digit |%c| matched to |%c| = %4d.",
Roman[i], T_Roman[j], T_Arabic[j]); */
if ((last_in == (in-1)) && (last_list > list))
Arabic = Arabic - 2*T_Arabic[last_list];
last_in = in;
last_list = list;
Arabic = Arabic + T_Arabic[list];
}
}
in=in+1;
}
//This part displays the results
printf("\nThe Roman number |%s| converts into Arabic %d.", Roman, Arabic);
//This part finishes the program
puts ("\nNormal end of program. BYE.");
//gotoxy(20,7); //Position at "character no", "line no"
printf("\n");
system("pause"); //DOS "Pause" command (for user to look at results)
}
