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/*
* FILE: lns.c
* Funciton: Count the sum of two large numbers
*/
/*
* Author: Wu Zhangjin, <zhangjinw@gmail.com>
* (c) 2006-11-25 dslab.lzu.edu.cn Lanzhou University
* License GPL Version 2
*/
#include <stdio.h> /* standard input/output functions */
#include <string.h> /* strlen function */
#define MAX_DIGITS 10000 /* define your max digit here */
/**
* sumof_ln - count the sum of two large numbers
* @ln_arr: the address of the array which store the two string of larger numbers
*
* Description:
* For the restrictions of the hardware, we can not count the sum of two
* large numbers directly, but we can use some skills to work it out.
* This function use a char array to store the large numbers, and then
* add every char digit with the carry, until the leftmost digit. Notes that
* if the digit of two numbers is not equal,The left aligned digit should be
* treated espectically--you should add a carry if it exist on every left digit.
* And also if the last carry exist,the leftmost digit should be '1'
*
* Returns:
* the address point of the string of sum
*
* Notes:
* you can define the maximum digit of the number by the macro MAX_DIGITS
*/
char* sumof_ln(char ln_arr[2][MAX_DIGITS])
{
int digit_arr[2], carry, sindex, lindex, i, tmp, align_lindex;
carry = 0;
digit_arr[0] = strlen(ln_arr[0]);
digit_arr[1] = strlen(ln_arr[1]);
sindex = (digit_arr[0] < digit_arr[1])?0:1;
lindex = 1 - sindex;
align_lindex = digit_arr[lindex] - digit_arr[sindex];
for (i = digit_arr[sindex] - 1; i >= 0; i --) {
tmp = ln_arr[lindex][align_lindex + i] + ln_arr[sindex][i] + carry;
ln_arr[lindex][align_lindex + i] = tmp - 48 - 10 * (carry = (tmp >= 106?1:0));
}
if (digit_arr[0] != digit_arr[1])
for (i = align_lindex - 1; i >= 0 && carry; i --) {
tmp = ln_arr[lindex][i] + carry;
ln_arr[lindex][i] = tmp - 10 * (carry = (tmp >= 58?1:0));
}
if (carry) {
for (i = digit_arr[lindex] - 1; i >= 0; i --)
ln_arr[lindex][i+1] = ln_arr[lindex][i];
ln_arr[lindex][digit_arr[lindex] + 1] = '\0';
ln_arr[lindex][0] = '1';
}
return ln_arr[lindex];
}
/**
* main - main function to call function sumof_ln
* Description:
* compile and link this c program and input two larger numbers, you can get the sum of them
*
* Notes:
* you cannot input a number whose digit is larger than MAX_DIGITS, but you can change by modifying the macro.
*/
int main(int argc, char *argv[])
{
char ln_arr[2][MAX_DIGITS];
printf("Please input two large numbers: \n");
scanf("%s %s", ln_arr[0], ln_arr[1]);
printf("The sum is:\n%s\n", sumof_ln( ln_arr ));
}
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