Give a string representing the date and ask what day of the year it is

#include <stdio.h>int monthday[] = { 0,                // (1)     31, 28, 31, 30, 31, 30,    31, 31, 30, 31, 30, 31    };int sumday[13];char str[100];int y, m, d;int main() {    int i;    while (scanf("%s", str) != EOF) {        sscanf(str, "%4d/%2d/%2d", &y, &m, &d);        if (y % 4 == 0 && y % 100 || y % 400 == 0) {            monthday[2] = 29;        // (2)        }        else {            monthday[2] = 28;        }        sumday[0] = 0;        for (i = 1; i <= 12; ++i) {  // (3)            sumday[i] = sumday[i - 1] + monthday[i];        }        int ans = sumday[m - 1] + d; // (4)        printf("%d\n", ans);    }    return 0;}

• $(1)$ Array monthday[i] It is stored in normal years , The first $i$ Total number of days in a month ;
• $(2)$ If it is a leap year according to the conditions ,2 The total number of days in a month becomes 29;
• $(3)$ Statistics $1$ Month to $i$ The total number of days of the month is stored in sumday[i] in ;
• $(4)$ Based on the previous month plus the current number of days , Calculate total days ;