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diff --git a/report-cls09.tex b/report-cls09.tex
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+\documentclass[xelatex,a4paper,11pt,ja=standard]{bxjsarticle}
+
+\usepackage{tex/preamble}
+\usepackage{tex/simple-title}
+
+\reportauthor{柴田健琉}
+\reporttitle{情報処理2 - 前期第9回課題}
+\reportdate{2026年}{06月}{16日}
+\turnindate{2026年}{06月}{16日}
+
+\begin{document}
+    \simpletitle
+
+    \section{はじめに}
+
+    この課題のプログラムは以下の環境での動作が確認されている:
+
+    \begin{itemize}
+        \item{OS: NixOS 26.05 Yarara, Linux 7.0.12 x86\_64}
+        \item{CC: GCC 15.2.0}
+        \item{CFLAGS: \texttt{-g -O1 -Wall -Wpedantic}}
+        \item{デバッガ: GNU gdb (GDB) 17.1}
+    \end{itemize}
+
+    \section{課題1 - 演習10-1}
+
+    教科書の演習10-1の\texttt{adjust\_point}関数を作成する.
+
+    \lstinputlisting[language=C,caption={課題1のプログラム}]{./src/cls09/a1.c}
+
+    \newpage
+
+    \subsection{実行結果}
+
+    \begin{figure}[tbh]
+        \centering
+        \includegraphics[width=10cm]{./assets/cls09-a1.png}
+        \caption{課題1の実行結果}
+    \end{figure}
+
+    \section{課題2 - 演習10-2}
+
+    教科書の演習10-2の\texttt{increment\_date}と\texttt{decrement\_date}関数を作成する. なお, 閏年は考慮しないものとする.
+
+    \lstinputlisting[language=C,caption={課題2のプログラム}]{./src/cls09/a2.c}
+
+    \subsection{実行結果}
+
+    \begin{figure}[tbh]
+        \centering
+        \includegraphics[width=10cm]{./assets/cls09-a2.png}
+        \caption{課題2の実行結果}
+    \end{figure}
+
+    \section{課題3 - 演習10-3}
+
+    教科書の演習10-3の\texttt{sort3}関数を作成する.
+
+    \lstinputlisting[language=C,caption={課題3のプログラム}]{./src/cls09/a3.c}
+
+    \subsection{実行結果}
+
+    \begin{figure}[tbh]
+        \centering
+        \includegraphics[width=10cm]{./assets/cls09-a3.png}
+        \caption{課題3の実行結果}
+    \end{figure}
+\end{document}
diff --git a/src/cls09/Makefile b/src/cls09/Makefile
new file mode 100644
index 0000000..feb36c8
--- /dev/null
+++ b/src/cls09/Makefile
@@ -0,0 +1,14 @@
+include ../common.mk
+
+PROJECT_NAME:=cls09
+
+TGTS:=$(patsubst %.c,%,$(wildcard *.c))
+
+all: $(TGTS)
+
+%: %.c
+	@mkdir -p $(BUILD_PATH)/$(PROJECT_NAME)
+	$(CC) $(CFLAGS) $^ -o $(BUILD_PATH)/$(PROJECT_NAME)/$@
+
+clean:
+	$(RM) -drf $(BUILD_PATH)/$(PROJECT_NAME)
diff --git a/src/cls09/a1.c b/src/cls09/a1.c
new file mode 100644
index 0000000..3f268cc
--- /dev/null
+++ b/src/cls09/a1.c
@@ -0,0 +1,21 @@
+#include <stdio.h>
+
+void adjust_point(int *n) {
+    if (*n < 0) {
+        *n = 0;
+    } else if (*n > 100) {
+        *n = 100;
+    }
+}
+
+int main(void) {
+    int d = 0;
+
+    printf("Input integer: ");
+    scanf("%d", &d);
+
+    adjust_point(&d);
+    printf("Result: %d\n", d);
+
+    return 0;
+}
diff --git a/src/cls09/a2.c b/src/cls09/a2.c
new file mode 100644
index 0000000..fe2f0cf
--- /dev/null
+++ b/src/cls09/a2.c
@@ -0,0 +1,76 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#define BUFFSZ 32
+
+const int DAYS_IN_MONTH[12] = {
+    31,
+    28,
+    31,
+    30,
+    31,
+    30,
+    31,
+    31,
+    30,
+    31,
+    30,
+    31
+};
+
+void increment_date(int *year, int *month, int *day) {
+    (*day)++;
+    
+    if (*day > DAYS_IN_MONTH[*month - 1]) {
+        *day = 1;
+        (*month)++;
+    }
+
+    if (*month > 12) {
+        *month = 1;
+        (*year)++;
+    }
+}
+
+void decrement_date(int *year, int *month, int *day) {
+    (*day)--;
+    
+    if (*day < 1) {
+        (*month)--;
+        if (*month < 1) {
+            *month = 12;
+            (*year)--;
+        }
+        *day = DAYS_IN_MONTH[*month - 1];
+    }
+}
+
+int main(void) {
+    char *buff = (char*)malloc(sizeof(char) * BUFFSZ);
+
+    int m, d, y;
+    printf("Input date in mm/dd/yyyy: ");
+    fgets(buff, BUFFSZ, stdin);
+    sscanf(buff, "%d/%d/%d", &m, &d, &y);
+
+
+    char opr_in;
+    while (1) {
+        printf("Select operation [+/-]: ");
+        opr_in = getc(stdin);
+        if (opr_in == '+') {
+            increment_date(&y, &m, &d);
+            printf("Tomorrow is %02d/%02d/%4d\n", m, d, y);
+            break;
+        } else if (opr_in == '-') {
+            decrement_date(&y, &m, &d);
+            printf("Yesterday was %02d/%02d/%4d\n", m, d, y);
+            break;
+        } else {
+            printf("Error: Please input correct operation mode.\n");
+        }
+    }
+
+
+    return 0;
+}
diff --git a/src/cls09/a3.c b/src/cls09/a3.c
new file mode 100644
index 0000000..f312f78
--- /dev/null
+++ b/src/cls09/a3.c
@@ -0,0 +1,26 @@
+#include <stdio.h>
+
+void swap(int *a, int *b) {
+    int t = *a;
+    *a = *b;
+    *b = t;
+}
+
+void sort3(int *x, int *y, int *z) {
+    if (*x > *y) swap(x, y);
+    if (*y > *z) swap(y, z);
+    if (*x > *y) swap(x, y);
+}
+
+int main(void) {
+    int a,b,c;
+
+    printf("Input 3 integers separated by ',': ");
+    scanf("%d,%d,%d", &a, &b, &c);
+
+    sort3(&a, &b, &c);
+
+    printf("Result: %d, %d, %d\n", a, b, c);
+
+    return 0;
+}