C language how concatenate 2 strings in another string to printf out?

Question

hello guys i need to concatenate 2 strings in another string and use it to printf out

char str1[20];
char str2[20];
char str3[40];

printf("type some txt");
scanf("%s", str1);
printf("again");
scanf("%s", str2);

// now I need to printf both strings in char str3[];

I know there are other ways to concatenate but I need to understand how I can do this one

I neeed a var for str3?
I need an operator?

thank u all , have nice day

Answer 1

C has tools for that in string.h!

#include <string.h>

strcpy(str3, str1); // copy str1 into str3
strcat(str3, str2); // append str2 to str3