Arithmetric Addition for 32-bit integer

[ernest]

I am trying to perform arithmetric addition for integers of more than 16-bits. The following is the code that I use but it does not allow SUM of variable 'a' and 'b' that exceed 16-bits ie. less than 65536 only.

What shall I do to allow it to calculate the SUM of more than 16-bit say 32 bits?

Cheers...

#include <16f877a.h>
//#device ICD=TRUE
#fuses HS,NOLVP,NOWDT,PUT
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)

#include <utility.c>
#include <stdlib.h>
#include <input.c>


#define GREEN_LED PIN_A5
#define YELLOW_LED PIN_B4
#define RED_LED PIN_B5
#define PUSH_BUTTON PIN_A4


main()
{

int32 a,b,result;
char opr;
int8 digits[7];
signed int8 counter;
int32 val;
int16 low;
int16 high;



setup_timer_0(RTCC_INTERNAL);
while(TRUE)
{
printf("\r\nEnter the first number: ");
a=get_long();

do
{
printf("\r\nEnter the operator (+-*/): ");
opr = getc();
}
while(!isamoung(opr,"+-*/"));

printf("\r\nEnter the second number: ");
b = get_long();

switch(opr)
{
case '+':
result = a + b;
break;

case '-':
result = a - b;
break;

case '*':
result = a * b;
break;

case '/':
result = a / b;
break;
}

/////////////////////////////////////////////////////////////////
val = a;

for (counter=7;counter>-1;counter--)
{
digits[counter]=val%10;
val=val/10;
}

low=result % 1000L;
high=result / 1000L;
printf("\r\nThe result is %lu%lu ",high,low);
// printf("\r\nVal= %d %d %d %d %d %d",digits[0],digits[1],digits[2],digits[3],digits[4],digits[5],digits[6]);

}

}

[Guest]

get_long() function returns 16-bit number (long is 16 bit wide in CCS C).
You have to modify the function to use atoi32() instead of atol() and return a 32-bit value:

signed int32 get_int32() {
char s[11];
signed int32 i;

get_string(s, 11); // able to get max. cca. 4 000 000 000

i=atoi32(s);
return(i);
}