diff --git a/pure-c-test/20220407/3-7.c b/pure-c-test/20220407/3-7.c
index e69de29..e1e6c92 100644
--- a/pure-c-test/20220407/3-7.c
+++ b/pure-c-test/20220407/3-7.c
@@ -0,0 +1,21 @@
+#include <stdio.h>
+#include <math.h>
+
+int main() {
+    int number = 0;
+    scanf("%d", &number);
+    
+    int length = 0;
+    while ((number % (int)pow(10, length)) != number) {
+        length ++;
+    }
+
+    int digital = 0, maxDigital = 0;
+    for (int i = 0; i < length; ++i) {
+        digital = number % 10;
+        maxDigital = digital > maxDigital ? digital : maxDigital;
+        number /= 10;
+    }
+
+    printf("%d", maxDigital);
+}
\ No newline at end of file
diff --git a/pure-c-test/20220407/3-8.c b/pure-c-test/20220407/3-8.c
index e69de29..813bfd1 100644
--- a/pure-c-test/20220407/3-8.c
+++ b/pure-c-test/20220407/3-8.c
@@ -0,0 +1,21 @@
+#include <stdio.h>
+
+int main() {
+    int n = 0;
+    scanf("%d", &n);
+
+    double numerator = 2.0,    //和分母
+            denominator = 1.0; //分子
+    
+    double oldNumerator = 0.0;
+
+    double result = 0.0;
+    for (int i = 0; i < n; ++i) {
+        result += numerator / denominator;
+        oldNumerator = numerator;
+        numerator += denominator;
+        denominator = oldNumerator;
+    }
+
+    printf("%.6f", result);
+}
\ No newline at end of file
diff --git a/pure-c-test/20220428/test-4-9.c b/pure-c-test/20220428/test-4-9.c
index e69de29..b717e50 100644
--- a/pure-c-test/20220428/test-4-9.c
+++ b/pure-c-test/20220428/test-4-9.c
@@ -0,0 +1,45 @@
+#include <stdio.h>
+#include <cstring>
+
+struct Student {
+    char name[16];
+    int score;
+};
+
+void sort(Student *students, int count);
+void copy(Student *target, Student *source);
+
+int main() {
+    int studentNumber = 0;
+    scanf("%d", &studentNumber);
+
+    Student students[studentNumber];
+    for (int i = 0; i < studentNumber; ++i) {
+        scanf("%s %d", students[i].name, &students[i].score);
+    }
+
+    sort(students, studentNumber);
+
+    for (Student student : students) {
+        printf("%s %d\n", student.name, student.score);
+    }
+}
+
+void sort(Student *students, int count) {
+    Student temp{};
+
+    for (int i = 0; i < count - 1; ++i) {
+        for (int j = 0; j < count - 1 - i; ++j) {
+            if (students[j].score < students[j + 1].score) {
+                copy(&temp, &students[j + 1]);
+                copy(&students[j + 1], &students[j]);
+                copy(&students[j], &temp);
+            }
+        }
+    }
+}
+
+void copy(Student *target, Student *source) {
+    strcpy(target->name, source->name);
+    target->score = source->score;
+}
\ No newline at end of file