Simplify struct declarations of C.

Use PascalCase for all structs in C.
SImplify n_queens.c
Format C code for chapter of graph.

codes/c/chapter_dynamic_programming/climbing_stairs_backtrack.c

@@ -28,7 +28,7 @@ int climbingStairsBacktrack(int n) {
     int choices[2] = {1, 2}; // 可选择向上爬 1 或 2 阶
     int state = 0;           // 从第 0 阶开始爬
     int *res = (int *)malloc(sizeof(int));
-    *res = 0;                // 使用 res[0] 记录方案数量
+    *res = 0; // 使用 res[0] 记录方案数量
     int len = sizeof(choices) / sizeof(int);
     backtrack(choices, state, n, res, len);
     int result = *res;