STRLEN() FUNCTION IN C

#include<string.h>
#include<stdio.h>
#include<conio.h>
main()
{
char str1[50],str2[50];
clrscr();
puts("String1 :");
gets(str1);
puts("String2 :");
gets(str2);
printf("\n Length Of The Given String is :%d",strlen(str1));
printf("\n Length Of The Given String is :%d\n",strlen(str2));
puts(strlwr(str1));
puts(strupr(str2));
getch();
}