using only one loop USACO Bronze February 2019 - Measuring Traffic

Problems and Contests
#1 
#include <stdio.h>
#include <algorithm>
#include <string.h>
#include <limits.h>

int main(void)
{
	freopen("traffic.in", "r", stdin);
	int m;
	scanf("%d", &m);

	struct {
		int a;
		int b;
	} end = {0, INT_MAX}, pre = {0, INT_MAX}, extra = {0, 0};
	bool first_none = false, next_nones = false;

	for (int i = 0; i < m; i++) {
		int p, q;
		char *s;
		scanf("%ms %d %d", &s, &p, &q);
		if (strcmp(s, "none") == 0) {
			end.a = std::max(p, end.a);
			end.b = std::min(q, end.b);
			if (!next_nones) {
				pre.a = end.a - extra.b;
				pre.b = end.b - extra.a;
				first_none = true;
			}
		}

		if (strcmp(s, "on") == 0) {
			extra.a += p;
			extra.b += q;
			if (first_none) {
				next_nones = true;
				end.a += p;
				end.b += q;
			}
		}

		if (strcmp(s, "off") == 0) {
			extra.a -= q;
			extra.b -= p;
			if (first_none) {
				next_nones = true;
				end.a -= q;
				end.b -= p;
			}
		}
	}
	pre.a = std::max(end.a - extra.b, pre.a);
	pre.b = std::min(end.b - extra.a, pre.b);
	
	if (pre.a < 0)
		pre.a = 0;
	if (end.a < 0)
		end.a = 0;
	if (pre.b < 0)
		pre.b = 0;
	if (end.b < 0)
		end.b = 0;
	freopen("traffic.out", "w", stdout);
	printf("%d %d\n%d %d", pre.a, pre.b, end.a, end.b);
}

I first_none = true when none has appeared for first time; next_nones = true when consecutive nones occurred the first time; if next_nones is false we find s = “none” we find the pre values. I calculate the extras from on/off till the end. After the for loop, since pre’s value can be tightened from end interval, we use extras struct for that purpsose.

But the code fails in two cases 4 and 7; in both only pre is wrong