C语言如何将两个字符串连接在一起？

1、使用str,需要引入string.h

#include <stdio.h>
#include <string.h>
int main(){
    char str1[101] = { 0 };
    char str2[50] = { 0 };
    gets(str1);
    gets(str2);
    strcat(str1, str2);
    puts(str1);
    return 0;
}

2、不用str

#include<stdio.h>
int main()
{
    char s1[100] = "I ";
    char s2[100] = "am a student";
    int i, j, n;
    for (i = 0; s1[i] != '\0'; i++)
        ;
    n = i;
    for (j = 0; s2[j] != '\0'; j++)
    {
        s1[n] = s2[j];
        n = n + 1;
    }
    s1[n] = '\0';
    printf("%s", s1);


}