diff --git a/.gitignore b/.gitignore
index 613cd88..c9c398f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 .intermediates/
+src/build
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diff --git a/report-cls12.tex b/report-cls12.tex
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+++ b/report-cls12.tex
@@ -0,0 +1,98 @@
+\documentclass[xelatex,a4paper,11pt,ja=standard]{bxjsarticle}
+
+\usepackage{tex/preamble}
+\usepackage{tex/simple-title}
+\usepackage{subcaption}
+
+\reportauthor{柴田健琉}
+\reporttitle{情報処理2 - 前期第12回課題}
+\reportdate{2026年}{07月}{07日}
+\turnindate{2026年}{07月}{12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 7.1.2 x86\_64}
+        \item{CC: GCC 15.2.0}
+        \item{CFLAGS: \texttt{-g -O1 -Wall -Wpedantic}}
+    \end{itemize}
+
+    \section{課題1}
+
+    授業資料内のサンプルコードに平均点数のエントリーを追加する.
+
+    \lstinputlisting[language=C]{./src/cls12/a1.c}
+
+    \subsection{実行結果}
+
+    \begin{figure}[tbh]
+        \centering
+        \includegraphics[width=12cm]{./assets/cls12-a1.png}
+        \caption{課題1の実行結果}
+    \end{figure}
+
+    \subsection{処理の流れ}
+
+    \begin{enumerate}
+        \item{構造体の配列\texttt{students}を宣言・定義する}
+        \item{\texttt{students}に対し, それぞれの要素の\texttt{english}, \texttt{mathematics}, \texttt{japanese}エントリーから平均を求め, \texttt{average}エントリーに代入}
+        \item{\texttt{students}の各要素の全エントリーを所定の書式に合わせて標準出力に表示させる}
+    \end{enumerate}
+
+    \subsection{書く際の難点}
+
+    ただ構造体にエントリーを1つ追加し, 平均値の計算を追加しただけなので特筆すべき難点はない.
+
+    \subsection{想定されるバグ}
+
+    浮動小数点数の誤差が考えられるが, 大抵は最小位の桁での誤差であり, また, 書式で小数点以下2桁しか表示しないので, 表示される数値に大きな誤差が生まれることはほとんど無い.
+
+    \newpage
+
+    \section{課題2}
+
+    課題1から平均点数を元に"A"から"D"までランク付けを行い, それぞれのランクの人数を記録する.
+
+    \lstinputlisting[language=C]{./src/cls12/a2.c}
+
+    \subsection{実行結果}
+
+    \begin{figure}[tbh]
+        \centering
+        \begin{minipage}[t]{0.95\textwidth}
+            \centering
+            \includegraphics[width=12cm]{./assets/cls12-a2-1.png}
+            \subcaption{Without \texttt{-D ALT\_DATA} Option}
+        \end{minipage}
+        \begin{minipage}[t]{0.95\textwidth}
+            \centering
+            \includegraphics[width=12cm]{./assets/cls12-a2-2.png}
+            \subcaption{With \texttt{-D ALT\_DATA} Option}
+        \end{minipage}
+        \caption{課題2の実行結果}
+    \end{figure}
+
+    \subsection{処理の流れ}
+
+    \begin{enumerate}
+        \item{構造体の配列\texttt{students}を宣言・定義する}
+        \item{\texttt{students}に対し, それぞれの要素の\texttt{english}, \texttt{mathematics}, \texttt{japanese}エントリーから平均を求め, \texttt{average}エントリーに代入}
+        \item{各ランクに属する人数を記録する整数型配列\texttt{grades}を宣言し, 0で初期化する}
+        \item{\texttt{students}に対し, 各要素の\texttt{average}エントリーの値の範囲を条件分岐で確認し, 文字型変数\texttt{grade}に対応するランクを代入し, \texttt{grades}の対応要素をインクリメントする}
+        \item{\texttt{students}の各要素の全エントリーとランクを所定の書式に合わせて標準出力に表示させる}
+        \item{\texttt{grades}の各要素を所定の書式に合わせて標準出力に表示させる}
+    \end{enumerate}
+
+    \subsection{書く際の難点}
+
+    課題1に分岐処理を追加するだけなので特筆すべき難点はない.
+
+    \subsection{想定されるバグ}
+
+    課題1同
+\end{document}
diff --git a/src/cls12/Makefile b/src/cls12/Makefile
new file mode 100644
index 0000000..146ca1d
--- /dev/null
+++ b/src/cls12/Makefile
@@ -0,0 +1,18 @@
+include ../common.mk
+
+PROJECT_NAME:=cls12
+
+TGTS:=$(patsubst %.c,%,$(wildcard *.c))
+
+all: $(TGTS) a2-alt
+
+%: %.c
+	@mkdir -p $(BUILD_PATH)/$(PROJECT_NAME)
+	$(CC) $(CFLAGS) $^ -o $(BUILD_PATH)/$(PROJECT_NAME)/$@
+
+a2-alt: a2.c
+	@mkdir -p $(BUILD_PATH)/$(PROJECT_NAME)
+	$(CC) $(CFLAGS) -D ALT_DATA $^ -o $(BUILD_PATH)/$(PROJECT_NAME)/$@
+
+clean:
+	$(RM) -drf $(BUILD_PATH)/$(PROJECT_NAME)
diff --git a/src/cls12/a1.c b/src/cls12/a1.c
new file mode 100644
index 0000000..86a8756
--- /dev/null
+++ b/src/cls12/a1.c
@@ -0,0 +1,41 @@
+#include <stdio.h>
+
+#define STUDENTS_NUM 4
+
+struct student {
+    char name[20];
+    int english;
+    int mathematics;
+    int japanese;
+    double average;
+};
+
+int main(void) {
+    struct student students[] = {
+        { .name = "佐藤", .english = 82, .mathematics = 72, .japanese = 58 },
+        { .name = "秋山", .english = 77, .mathematics = 82, .japanese = 79 },
+        { .name = "永田", .english = 52, .mathematics = 62, .japanese = 39 },
+        { .name = "藤田", .english = 61, .mathematics = 82, .japanese = 88 }
+    };
+
+    for (int i = 0; i < STUDENTS_NUM; i++) {
+        students[i].average = (double)(
+            students[i].english +
+            students[i].mathematics +
+            students[i].japanese
+        ) / 3.f;
+    }
+
+    for (int i = 0; i < STUDENTS_NUM; i++) {
+        printf(
+            "%10s: 英語=%3d\t数学=%3d\t国語=%3d\t平均=%.2lf\n",
+            students[i].name,
+            students[i].english,
+            students[i].mathematics,
+            students[i].japanese,
+            students[i].average
+        );
+    }
+
+    return 0;
+}
diff --git a/src/cls12/a2.c b/src/cls12/a2.c
new file mode 100644
index 0000000..224221a
--- /dev/null
+++ b/src/cls12/a2.c
@@ -0,0 +1,73 @@
+#include <stdio.h>
+
+#define STUDENTS_NUM 4
+
+struct student {
+    char name[20];
+    int english;
+    int mathematics;
+    int japanese;
+    double average;
+};
+
+int main(void) {
+#ifdef ALT_DATA
+    struct student students[] = {
+        { .name = "佐藤", .english = 89, .mathematics = 86, .japanese = 78 },
+        { .name = "秋山", .english = 78, .mathematics = 65, .japanese = 79 },
+        { .name = "永田", .english = 64, .mathematics = 33, .japanese = 53 },
+        { .name = "藤田", .english = 89, .mathematics = 47, .japanese = 62 }
+    };
+#else
+    struct student students[] = {
+        { .name = "佐藤", .english = 82, .mathematics = 72, .japanese = 58 },
+        { .name = "秋山", .english = 77, .mathematics = 82, .japanese = 79 },
+        { .name = "永田", .english = 52, .mathematics = 62, .japanese = 39 },
+        { .name = "藤田", .english = 61, .mathematics = 82, .japanese = 88 }
+    };
+#endif
+
+    for (int i = 0; i < STUDENTS_NUM; i++) {
+        students[i].average = (double)(
+            students[i].english +
+            students[i].mathematics +
+            students[i].japanese
+        ) / 3.f;
+    }
+
+    int grades[4] = {0};
+    for (int i = 0; i < STUDENTS_NUM; i++) {
+        char grade = 0;
+        int avg = students[i].average;
+        if (avg < 60) {
+            grade = 'D';
+            grades[3]++;
+        } else if (avg >= 60 && avg < 70) {
+            grade = 'C';
+            grades[2]++;
+        } else if (avg >= 70 && avg < 80) {
+            grade = 'B';
+            grades[1]++;
+        } else {
+            grade = 'A';
+            grades[0]++;
+        }
+        printf(
+            "%10s: 英語=%3d\t数学=%3d\t国語=%3d\t平均=%.2lf\t成績=%c\n",
+            students[i].name,
+            students[i].english,
+            students[i].mathematics,
+            students[i].japanese,
+            students[i].average,
+            grade
+        );
+    }
+
+    printf("成績: ");
+    for (int i = 0; i < 4; i++) {
+        printf("%c=%d人\t", 'A' + i, grades[i]);
+    }
+    putchar('\n');
+
+    return 0;
+}