diff --git a/homework/11989.c b/homework/11989.c
new file mode 100644
index 0000000..8501a16
--- /dev/null
+++ b/homework/11989.c
@@ -0,0 +1,58 @@
+#include <stdio.h>
+
+void DigiTran(int k, char res[]);
+
+int s;
+
+int main() {
+    while (scanf("%d", &s)) {
+        if (s == -1) {
+            return 0;
+        }
+        char res[233];
+        DigiTran(s, res);
+        printf("%s ", res);
+    }
+}
+
+int ws(int a) {
+    int ans = 0;
+    while (a) {
+        ans++;
+        a /= 10;
+    }
+    return ans;
+}
+
+void DigiTran(int k, char res[]) {
+    int rr[233];
+    if (k == 0) {
+        res[0] = 'A';
+        res[1] = '\0';
+        return;
+    }
+    int n = ws(k);
+    for (int i = 0; i < n; i++) {
+        rr[n - i - 1] = k % 10;
+        k /= 10;
+    }
+    // rr 为将数组拆解为一位一位的数组
+    int ki = 0;  // 标识 res 位数
+    for (int i = 0; i < n; i++) {
+        if (i == n - 1) {
+            res[ki++] = rr[i] + 'A';
+            continue;
+        }
+        int ls = rr[i] * 10 + rr[i + 1];
+        // 如果两位数字符合条件
+        if (ls >= 10 && ls <= 25) {
+            res[ki++] = ls + 'A';
+            i++;
+            // 替换两位需要将 i++
+        } else {
+            //如果不符合，只用一位变换
+            res[ki++] = rr[i] + 'A';
+        }
+    }
+    res[ki] = '\0';
+}
\ No newline at end of file