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diff --git a/out/report-cls05.pdf b/out/report-cls05.pdf
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diff --git a/report-cls05.tex b/report-cls05.tex
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+++ b/report-cls05.tex
@@ -0,0 +1,68 @@
+\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5回課題}
+\reportdate{2026年}{05月}{21日}
+\turnindate{2026年}{05月}{21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 25.11 Xantusia, Linux 7.0.6 x86\_64}
+        \item {CC: GCC 15.2.0}
+        \item {CFLAGS: \texttt{-g -O1 -Wall -Wpedantic}}
+        \item {ファイルエンコーディング: UTF-8}
+    \end{itemize}
+
+    \section{課題1}
+
+    与えられた文字列内を探索し，特定の文字の最初に表れる添字を返す関数\texttt{str\_char}を作成する，
+
+    \lstinputlisting[language=C,title={課題1のプログラム}]{./src/cls05/a1.c}
+
+    \subsection{実行結果}
+
+    \begin{figure}[tbh]
+        \centering
+        \includegraphics[width=12cm]{./assets/cls05-a1.png}
+        \caption{課題1の実行結果}
+    \end{figure}
+
+    \section{課題2}
+
+    入力された文字列の文字と文字コードを表示するプログラム，なお文字列の入力には\texttt{getchar}関数を用いること．
+
+    \lstinputlisting[language=C,title={課題2のプログラム}]{./src/cls05/a2.c}
+
+    \subsection{実行結果}
+
+    \begin{figure}[tbh]
+        \centering
+        \includegraphics[width=12cm]{./assets/cls05-a2.png}
+        \caption{課題2の実行結果}
+    \end{figure}
+
+    \section{課題3}
+
+    入力した文字列の並びを反転させる関数\texttt{rev\_string}を作成する．
+
+    \lstinputlisting[language=C,title={課題3のプログラム}]{./src/cls05/a3.c}
+
+    \newpage
+
+    \subsection{実行結果}
+
+    \begin{figure}[tbh]
+        \centering
+        \includegraphics[width=12cm]{./assets/cls05-a3.png}
+        \caption{課題3のプログラム}
+    \end{figure}
+\end{document}
diff --git a/src/cls05/Makefile b/src/cls05/Makefile
new file mode 100644
index 0000000..388929e
--- /dev/null
+++ b/src/cls05/Makefile
@@ -0,0 +1,14 @@
+include ../common.mk
+
+PROJECT_NAME:=cls05
+
+TGTS:=$(patsubst %.c,%,$(wildcard *.c))
+
+all: $(TGTS)
+
+%: %.c
+	@mkdir -p $(BUILD_PATH)/$(PROJECT_NAME)
+	$(CC) $(CFLAGS) -I. $^ -o $(BUILD_PATH)/$(PROJECT_NAME)/$@
+
+clean:
+	$(RM) -drf $(BUILD_PATH)/$(PROJECT_NAME)
diff --git a/src/cls05/a1.c b/src/cls05/a1.c
new file mode 100644
index 0000000..e8202a8
--- /dev/null
+++ b/src/cls05/a1.c
@@ -0,0 +1,38 @@
+#include <stdio.h>
+
+#define BUFF_SZ 256
+
+int str_char(const char s[], int c) {
+    int idx = 0;
+    while (s[idx] != '\0') {
+        if (s[idx] == (char)c) {
+            return idx + 1;
+        }
+        idx++;
+    }
+
+    return -1;
+}
+
+int main(void) {
+    char buff[BUFF_SZ] = {0};
+    char query = 0;
+    
+    printf("Input String: ");
+    fgets(buff, BUFF_SZ, stdin);
+
+    printf("Input Search Character: ");
+    scanf("%c", &query);
+
+    printf("%c, %s\n", query, buff);
+
+    int ret = str_char(buff, query);
+    if (ret != -1) {
+        printf("Found %c at %d\n", query, ret);
+    } else {
+        printf("Queried character not found.\n");
+    }
+
+    return 0;
+}
+
diff --git a/src/cls05/a2.c b/src/cls05/a2.c
new file mode 100644
index 0000000..1d68e32
--- /dev/null
+++ b/src/cls05/a2.c
@@ -0,0 +1,25 @@
+#include <stdio.h>
+
+#define BUFF_SZ 256
+
+int main(void) {
+    char buff[BUFF_SZ] = {0};
+    int cnt = 0;
+
+    printf("Input String: ");
+    while ((buff[cnt] = getchar()) != '\n') {
+        cnt++;
+    };
+    buff[cnt] = '\0';
+
+    int i = 0;
+    while (buff[i] != '\0') {
+        printf(
+            "Char: %c, ASCII Code: 0x%X (%d)\n",
+            buff[i], (int)buff[i], (int)buff[i]
+        );
+        i++;
+    }
+
+    return 0;
+}
diff --git a/src/cls05/a3.c b/src/cls05/a3.c
new file mode 100644
index 0000000..99b495c
--- /dev/null
+++ b/src/cls05/a3.c
@@ -0,0 +1,34 @@
+#include <stdio.h>
+
+#define BUFF_SZ 256
+
+void rev_string(char s[]) {
+    int str_sz = 0;
+    char tmp = 0;
+
+    do {
+        str_sz++;
+    } while (s[str_sz] != '\0' && str_sz < BUFF_SZ);
+    str_sz--; // remove null terminater from count
+
+    for (int i = 0; i < str_sz/2; i++) {
+        tmp = s[str_sz - 1 - i];
+        s[str_sz - 1 - i] = s[i];
+        s[i] = tmp;
+    }
+}
+
+int main(void) {
+    char buff[BUFF_SZ] = {0};
+
+    printf("Input String: ");
+    fgets(buff, BUFF_SZ, stdin);
+
+    printf("Got: %s\n", buff);
+
+    rev_string(buff);
+
+    printf("Rev: %s\n", buff);
+
+    return 0;
+}