Chap10[D]c Automobile has weird serial numbers

An automobile company has serial number for engine parts starting from AA0 to FF9. The other characteristics of parts to be specified in a structure are: Year of manufacture, material and quantity manufactured.
(a) Specify a structure to store information corresponding to a part.
(b) Write a program to retrieve information on parts with serial numbers between BB1 and CC6.

***When keying in the parts key alphabets in uppercase.

void main()
{
int i,j,letter,a,b,c,d;
char m[3],n[3],q[1];

struct parts
{
int year;
char material[20];
int qty;
};

struct parts p[27]={
{1991,"rubber",5},{1992,"rubber",6},{1991,"metal",7},{1997,"wood",8},{1993,"plastic",9},{1992,"wood",6},{1997,"metal",6},{1992,"rubber",7},{1991,"wood",2},
{1992,"metal",6},{1995,"wood",4},{1992,"rubber",5},{1998,"wood",2},{1997,"plastic",8},{1998,"plastic",9},{1998,"metal",8},{1991,"metal",8},{1992,"wood",5},
{1993,"wood",8},{1993,"rubber",7},{1997,"metal",2},{1998,"wood",1},{1999,"plastic",8},{1995,"wood",6},{1990,"rubber",3},{1997,"plastic",9},{1998,"wood",7}
};

/* for(i=0,letter=65;i<2;i++,letter++)
{
for(j=0;j<9;j++)
{
printf("\Key in values for year,material and quantity respectively for part %c%c%d\n",letter,letter,j+1);
scanf("%d%s%d",&p[i][j].year,&p[i][j].material,&p[i][j].qty);
}
} */

while(1)
{
clrscr();

printf("\nKey in the part number to retrieve the information from\n");
scanf("%s",m);
printf("\nKey the part number till the information is retrieved(End)\n");
scanf("%s",n);

a=((m[0]-65)*9+(m[2]-49));
b=((n[0]-65)*9+(n[2]-49));
printf("\na is %d,\nb is %d,\nm[0] is %d, n[0] is %d",a,b,m[0],n[0]);
c=a;
d=a;
while(c>=9)
{
c-=9;

}
printf("\nc after while is %d",c);
while( d>9)
d-=9;



for(i=a;i<=b;i++,c++,d++)
{
if(c==9)
{
m[0]+=1;
c=0;
}
if(d==9)
{
d=0;
}
printf("\nPart: %c%c%d, Year: %d, Material: %s, Quantity: %d",m[0],m[0],d+1,p[i].year,p[i].material,p[i].qty);
}






printf("\nKey q to quit or any other key to continue\n");
scanf("%s",q);

if(q[0]==113)
break;
}
}