diff --git "a/data/3.C\350\257\255\350\250\200\351\253\230\351\230\266/3.\344\275\215\350\277\220\347\256\227/2.\344\272\214\350\277\233\345\210\266\346\225\260/count.md" "b/data/3.C\350\257\255\350\250\200\351\253\230\351\230\266/3.\344\275\215\350\277\220\347\256\227/2.\344\272\214\350\277\233\345\210\266\346\225\260/count.md"
new file mode 100644
index 0000000000000000000000000000000000000000..834656c59561a69dff895ad87f80487f1b15e594
--- /dev/null
+++ "b/data/3.C\350\257\255\350\250\200\351\253\230\351\230\266/3.\344\275\215\350\277\220\347\256\227/2.\344\272\214\350\277\233\345\210\266\346\225\260/count.md"
@@ -0,0 +1,74 @@
+# 计算位数
+
+计算整数的二进制形式有多少位。
+
+## template
+
+```c
+#include <stdio.h>
+
+$code
+
+int main(char** args){
+    printf("bits(%d) has %d bits\n", 100, bits(100));
+    printf("bits(%d) has %d bits\n", 32, bits(32));
+    printf("bits(%d) has %d bits\n", 10, bits(10));
+    printf("bits(%d) has %d bits\n", 25, bits(25));
+    printf("bits(%d) has %d bits\n", 7, bits(7));
+    return 0;
+}
+```
+
+## 答案
+
+```c
+unsigned int bits(unsigned int x){
+    unsigned int n = 0;
+    while(x){
+        x >>= 1;
+        n++;
+    }
+    return n;
+}
+```
+
+## 选项
+
+### 位移计算没有保存
+
+```c
+unsigned int bits(unsigned int x){
+    unsigned int n = 0;
+    while(x){
+        x >> 1;
+        n++;
+    }
+    return n;
+}
+```
+
+### 没有括号导致流程错误
+
+```c
+unsigned int bits(unsigned int x){
+    unsigned int n = 0;
+    while(x)
+        x >>= 1;
+        n++;
+
+    return n;
+}
+```
+
+### 运算符错误
+
+```c
+unsigned int bits(unsigned int x){
+    unsigned int n = 0;
+    while(x){
+        x << 1;
+        n++;
+    }
+    return n;
+}
+```
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