add some demo

hundred_chicken.c

@@ -0,0 +1,34 @@
+#include <stdio.h>
+
+/*
+ * 三种鸡单价分别为 R, S, 1/T，其中 R > S
+ * 花 M 钱买 N 只
+ */
+void calc(int R, int S, int T, int M, int N)
+{
+    int v = 0;
+    int r = 1;
+    for (; r < N && r * R < M; r++) {
+        int m = M - R * r;
+        int n = N - r;
+        if (m >= n * S || m * T <= n) continue;
+
+        int a = T * m - n;
+        int b = T * (S * n - m);
+        int c = S * T - 1;
+        if (a < 0 || b < 0 || a % c || b % c) continue;
+
+        int s = a / c;
+        int t = b / c;
+        printf("----- %d -----\n", ++v);
+        printf("%d + %d + %d = %d\n", r, s, t, N);
+        printf("%d * %d + %d * %d + %d / %d = %d\n", r, R, s, S, t, T, M);
+    }
+}
+
+
+int main()
+{
+    calc(5, 3, 3, 100, 100);
+    return 0;
+}

number_to_pinyin.c

@@ -0,0 +1,31 @@
+#include <stdio.h>
+
+char *map[] = {
+    "ling", "yi", "er", "san", "si",
+    "wu", "liu", "qi", "ba", "jiu"
+};
+
+void display_num_with_pinyin(int num)
+{
+    char *stack[10] = {0,};
+    int stack_top = 0;
+    char *sign = "";
+    if (num < 0) {
+        sign = "fu ";
+        num = -num;
+    }
+    for (; num; num = num / 10) {
+        stack[stack_top++] = map[num % 10];
+    }
+    printf("%s", sign);
+    while (--stack_top > -1) {
+        printf("%s ", stack[stack_top]);
+    }
+    printf("\b\n");
+}
+
+int main()
+{
+    display_num_with_pinyin(-6543210);
+    return 0;
+}

simplify_the_denominator.c

@@ -0,0 +1,22 @@
+#include <stdio.h>
+
+int gcd(int a, int b)
+{
+    return (b == 0) ? a : gcd(b, a % b);
+}
+
+int show_simplified(int a, int b)
+{
+    if (!a || !b) return printf("a, b should not be zero!\n");
+    int sign = (a > 0) ^ (b > 0);
+    a = (a > 0) ? a : -a;
+    b = (b > 0) ? b : -b;
+    int d = gcd(a, b);
+    return printf("simplified is: %s%d/%d\n", sign ? "-" : "", a / d, b / d);
+}
+
+int main()
+{
+    show_simplified(123, 333);
+    return 0;
+}