c concatenate strings

char str[80];
strcpy(str, "these ");
strcat(str, "strings ");
strcat(str, "are ");
strcat(str, "concatenated.");- (NSString *)strCat: (NSString *)one: (NSString *)two
{
    NSString *myString;
    myString = [NSString stringWithFormat:@"%@%@", one , two];
    return myString;
}
#include <stdio.h>
#include <string.h>
int main() {
	char str[80];
strcpy(str, "these ");
strcat(str, "strings ");
strcat(str, "are ");
strcat(str, "concatenated.");
printf("%s\n", str);
}#include <stdio.h>
#include <string.h>
int main()
{
  char a[1000], b[1000];

  printf("Enter the first string\n");
  gets(a);

  printf("Enter the second string\n");
  gets(b);

  strcat(a, b);

  printf("String obtained on concatenation: %s\n", a);

  return 0;
}// null protected
char* strconcat(char *str1, const char *str2)
{
	char *str = NULL;
    size_t len1 = 0;
    size_t len2 = 0;

	if (str1)
    	len1 = strlen(str1);
    if (str2)
    	len2 = strlen(str2);
    if (!(str = calloc(sizeof(char), (len1 + len2 + 1))))
        return NULL;
    if (str1)
        memcpy(str, str1, len1);
    if (str2)
        memcpy(str + len1, str2, len2);
    return (str);
}