[Warning] incompatible implicit declaration of built-in function ‘strcat’

After watching the machine learning course today, I changed to Learn C language for a while. It was also the first time I encountered the strcat function, the string concatenation function. Its general form is strcat (character array 1, character array 2). The function concatenates the strings of two character arrays, attaches string 2 to the end of string 1, and places the result in character array 1. The function call returns a function value — the address of character array 1. Such as:

#include<stdio.h>
int main()
{
	char str1[30] = {"People's Republic of "};
	char str2[] = {"China"};
	printf("%s",strcat(str1,str2));
	
	return 0;
}

Output code error:

In function 'main':
[Warning] incompatible implicit declaration of built-in function 'strcat'

Baidu once reason, little added header file

#include<stdlib.h>

#include<string.h>

After adding, the program output is normal:


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