Strlen and sizeof, array length and string length, don't be silly

This article mainly talks about many new acquaintances C Language students will encounter problems , It is also a must for many colleges and universities to take the postgraduate entrance examination .sizeof and strlen How to use it , I briefly summarized their usefulness ：

sizeof: Calculate variable size , Array size ,（ Include \0） The unit is byte , Is an operator ; strlen： Calculate string length , With \0 For the end sign , It's a library function .

Let's start with a piece of code ：

int main()
{
    
	char a[] = "xyz";
	char b[] = {
     'x','y','z' };
    printf("%d\n",sizeof(a));    //4
    printf("%d\n",sizeof(b));    //3
    printf("%d\n",strlen(a));    //3
    printf("%d\n",strlen(b));    //>=3
	return 0;
}

By now everyone should be able to understand ,strlen Is the number of number characters , As long as we don't meet \0, Then count back ; and sizeof Is the number size , How big is this array or variable , Unit is byte , It's the number of bytes , Be careful \0 It's also a character .
Let's take a look at a real topic for the postgraduate entrance examination ：

This topic , The answer is C, Note that the array length calculation formula is size=sizeof(arr)/sizeof(arr[0])
therefore a The length of is 4,（ because a There is..., by default \0）b The length of is 3.

I hope it can help you in your study C Language students .