//exercise 1: a simple C program 
//http://e...content-available-to-author-only...u.tw/~klim/unix-p/usp-1092.html
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
	char *ptr, c;
	char *str = malloc(sizeof(char) * 256 + 1);
	char *num = malloc(sizeof(char) * 16 + 1);
	int i = 0, j = 0, len;
	long sum = 0;
 
	while ((c = getchar()) != EOF) {
		str[i] = c;
		i++;
	}
	str[i] = '\0';
	for (i = 0; i <= strlen(str); i++) {
		num[j] = str[i];
		j++;
		if ((str[i] == 32) || (str[i] == '\n')) {
			num[j] = '\0';
			if ((num[0] == '\0') || (num[0] < 48) || (num[0] > 57)) {
				char *num = "0";
			}
			else {
				sum = sum + strtol(num, &ptr, 10);
			}
			j = 0;
		}	
	}
	printf("\n%ld\n", sum);
}
 

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I have 1000
You have 200
I give you 50
Now You have 250.