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+/*
+Challenge 138
+
+TASK #1 > Workdays
+Submitted by: Mohammad S Anwar
+You are given a year, $year in 4-digits form.
+
+Write a script to calculate the total number of workdays in the given year.
+
+For the task, we consider, Monday - Friday as workdays.
+
+Example 1
+Input: $year = 2021
+Output: 261
+Example 2
+Input: $year = 2020
+Output: 262
+*/
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+enum { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday };
+
+int day_of_week(int y, int m, int d) {
+    return (d += m < 3 ? y-- : y - 2, 23*m/9 + d + 4 + y/4- y/100 + y/400)%7;
+}
+
+bool is_leap_year(int y) {
+    return y%400==0 ? true : y%100==0 ? false : y%4==0 ? true : false;
+}
+
+int days_of_month(int y, int m) {
+    switch (m) {
+        case 1: case 3: case 5: case 7: case 8: case 10: case 12: return 31;
+        case 4: case 6: case 9: case 11: return 30;
+        case 2: return is_leap_year(y) ? 29 : 28;
+        default: assert(0);
+    }
+}
+
+int num_workdays(int y) {
+    int wd = 0;
+    for (int m = 1; m <= 12; m++) {
+        int dom = days_of_month(y, m);
+        for (int d = 1; d <= dom; d++) {
+            int dow = day_of_week(y, m, d);
+            if (dow != Sunday && dow != Saturday)
+                wd++;
+        }
+    }
+    return wd;
+}
+
+int main(int argc, char* argv[]) {
+    if (argc != 2) {
+        fputs("usage: ch-1 year", stderr);
+        return EXIT_FAILURE;
+    }
+
+    int y = atoi(argv[1]);
+    printf("%d\n", num_workdays(y));
+}