diff --git a/【额外练习】选择结构/7-33 选择-三数排序.c b/【额外练习】选择结构/7-33 选择-三数排序.c
new file mode 100644
index 0000000..f2069c5
--- /dev/null
+++ b/【额外练习】选择结构/7-33 选择-三数排序.c	
@@ -0,0 +1,29 @@
+#include <stdio.h>
+
+int main() {
+    int a, b, c;
+
+    scanf("%d%d%d", &a, &b, &c);
+
+    if (a > b) {
+        int temp = a;
+        a = b;
+        b = temp;
+    }
+
+    if (a > c) {
+        int temp = a;
+        a = c;
+        c = temp;
+    }
+
+    if (b > c) {
+        int temp = b;
+        b = c;
+        c = temp;
+    }
+
+    printf("%d %d %d\n", a, b, c);
+
+    return 0;
+}
diff --git a/【额外练习】选择结构/7-34 选择-凯撒密码.c b/【额外练习】选择结构/7-34 选择-凯撒密码.c
new file mode 100644
index 0000000..c7d8487
--- /dev/null
+++ b/【额外练习】选择结构/7-34 选择-凯撒密码.c	
@@ -0,0 +1,19 @@
+#include <stdio.h>
+
+int main() {
+    char c;
+
+    scanf("%c", &c);
+
+    if (c >= 'a' && c <= 'z') {
+        c += 3;
+        if (c > 'z') c -= 26;
+    } else if (c >= 'A' && c <= 'Z') {
+        c += 3;
+        if (c > 'Z') c -= 26;
+    }
+
+    printf("%c\n", c);
+
+    return 0;
+}
diff --git a/【额外练习】选择结构/7-35 选择-简单的运算Ⅱ.c b/【额外练习】选择结构/7-35 选择-简单的运算Ⅱ.c
new file mode 100644
index 0000000..b14b835
--- /dev/null
+++ b/【额外练习】选择结构/7-35 选择-简单的运算Ⅱ.c	
@@ -0,0 +1,27 @@
+#include <stdio.h>
+
+int main() {
+    double a, b, c;
+
+    scanf("%lf%lf%lf", &a, &b, &c);
+
+    if (a == 0) {
+        if (b == 0 && c != 0) {
+            printf("0\n");
+        } else {
+            printf("1\n");
+        }
+    } else {
+        double delta = b * b - 4 * a * c;
+
+        if (delta > 0) {
+            printf("2\n");
+        } else if (delta == 0) {
+            printf("1\n");
+        } else {
+            printf("0\n");
+        }
+    }
+
+    return 0;
+}
diff --git a/【额外练习】选择结构/7-36 选择-三角形和圆.c b/【额外练习】选择结构/7-36 选择-三角形和圆.c
new file mode 100644
index 0000000..2092398
--- /dev/null
+++ b/【额外练习】选择结构/7-36 选择-三角形和圆.c	
@@ -0,0 +1,26 @@
+#include <math.h>
+#include <stdio.h>
+
+int main() {
+    double a, b, c, r;
+
+    scanf("%lf%lf%lf%lf", &a, &b, &c, &r);
+
+    double s = (a + b + c) / 2.0;
+
+    if (s <= a || s <= b || s <= c) {
+        printf("No\n");
+        return 0;
+    }
+
+    double area = sqrt(s * (s - a) * (s - b) * (s - c));
+    double inRadius = area / s;
+
+    if (r <= inRadius) {
+        printf("Yes\n");
+    } else {
+        printf("No\n");
+    }
+
+    return 0;
+}
diff --git a/【额外练习】选择结构/7-38 选择-百分制转五分制.c b/【额外练习】选择结构/7-38 选择-百分制转五分制.c
new file mode 100644
index 0000000..23ef499
--- /dev/null
+++ b/【额外练习】选择结构/7-38 选择-百分制转五分制.c	
@@ -0,0 +1,23 @@
+#include <stdio.h>
+
+int main() {
+    int t;
+
+    scanf("%d", &t);
+
+    if (t >= 90 && t <= 100) {
+        printf("A\n");
+    } else if (t >= 80 && t <= 89) {
+        printf("B\n");
+    } else if (t >= 70 && t <= 79) {
+        printf("C\n");
+    } else if (t >= 60 && t <= 69) {
+        printf("D\n");
+    } else if (t >= 0 && t <= 59) {
+        printf("E\n");
+    } else {
+        printf("Score is error!\n");
+    }
+
+    return 0;
+}