Interesting questions about C

Today, I went to a company to take the test. I personally felt that there were several interesting questions. I would like to share them with you:

1,

void main(){unsigned char i =0;char a[1024] ={0};for(i = 0;i<1024;i++){printf("a[%d]:0x%02x\n",i,a[i]);}}

What is the output result?

The answer should be: 1. endless loop, and then

A [0]: 0x00

A [1]: 0x00

A [2]: 0x00

......

 

A [255]: 0x00

 

Note that the maximum value of I is 255, so it will keep repeating.

 

2,

void main(){int a =0;a|=(0x01<<4);printf("%d\n",a);//a=16;a&=~(0x01<<4);printf("%d\n",a);//a=0;}

You can calculate it by yourself.

3,

void main(){int a =1;printf("%d\n",*((unsigned char *)&a));//output is 1a=0x12345678;printf("%d\n",*((unsigned char *)&a+1));//output is 86}

The second output is 86, which is not clear yet.

 

4,

void function1(char*a){printf("%d\n",strlen(a));}void function2(char*a){printf("%d\n",sizeof(a));}void main(){char a[100] ={0};//0 is '\0' function1(a);// 0 is '\0' ,so strlen(a) is 0;function2(a);// pointer length is 4 bytes;}

Function1 is printed as 0, because a [100] is initialized to 0, 0 is '\ 0 '.

Function2 prints 4, which is the length of the pointer type.

5,

void main(){char a[8] ={"hello"};char b[8]={0};printf("a:0x%08x\n",a);strcpy(b,"01234567");printf("a:%s\n",a);printf("b:%s\n",b);}

The result is:
A: 0xbfc2dccc
A:
B: 01234567
I haven't figured it out yet.

 

6,

Unsigned int A = 10; // when unsigned, the highest bit is not used to indicate positive and negative. Int B =-100; // 1 of the highest bit of int indicates a negative number if (a + B> 10) // A + B is added only when all values are converted to the unsigned type, so> 10 printf ("> 10 \ n"); elseprintf ("<10 \ n ");

Print "> 10 ".

 

7,

void main(){char a[10]; printf("%d\n",strlen(a) );}

The output is not 10, because strlen (a) ends when it finds '\ 0'. We do not know where the end mark' \ 0' of a [10] is.