Add multilingual exercise code (#1959)

Replace the exercise pages' Python-only snippets with source-backed implementations for the 13 visible programming languages, and localize reader-facing comments by site language. Zig remains out of scope.

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codes/c/chapter_computational_complexity/complexity_exercises.c

@@ -0,0 +1,61 @@
+/**
+ * File: complexity_exercises.c
+ * Created Time: 2026-08-18
+ * Author: Hello Algo Team
+ */
+
+#include <assert.h>
+
+/* 迭代求和 */
+int sumIter(int n) {
+    int res = 0;
+    for (int i = 1; i <= n; i++) {
+        res += i;
+    }
+    return res;
+}
+
+/* 递归求和 */
+int sumRecur(int n) {
+    if (n == 1) {
+        return 1;
+    }
+    return n + sumRecur(n - 1);
+}
+
+/* 线性阶循环 */
+int linearLoop(int n) {
+    int res = 0;
+    for (int i = 0; i < n; i++) {
+        res += i;
+    }
+    return res;
+}
+
+/* 平方阶循环 */
+int quadraticLoop(int n) {
+    int res = 0;
+    for (int i = 0; i < n; i++) {
+        for (int j = i; j < n; j++) {
+            res += j;
+        }
+    }
+    return res;
+}
+
+/* 对数阶循环 */
+int logarithmicLoop(int n) {
+    while (n > 1) {
+        n /= 2;
+    }
+    return n;
+}
+
+int main(void) {
+    assert(sumIter(1) == 1 && sumRecur(1) == 1);
+    assert(sumIter(4) == 10 && sumRecur(4) == 10);
+    assert(linearLoop(4) == 6);
+    assert(quadraticLoop(4) == 20);
+    assert(logarithmicLoop(4) == 1 && logarithmicLoop(5) == 1);
+    return 0;
+}