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