String operation

#include<stdio.h>
#include<conio.h>
#include<string.h>
int STRLEN(char*);
int STRCPY(char*,char*);
int STRCMP(char*,char*);
int STRCAT(char*,char*,char*);
int STRREV(char*);
void main()
{
	int c;
	char str[20],str1[10],str2[10],str3[20];
	clrscr();
	re:
	printf("
Enter choice=>");
	printf("
		1:string len.
		2:string copy
		3:string
cmp.
		4:string cat.
		5:string rev.");
	printf("
		6:for exit=>");
	scanf("%d",&c);switch(c)
	{
		case 1:
			printf("Enter the string=>");
			scanf("%s",&str1);
			printf("string length=>%d
",STRLEN(str1));
			break;
		case 2:
			printf("
Enter the string=>");
			scanf("%s",str1);
			STRCPY(str2,str1);
			printf("copied string=>");
			puts(str2);
			break;
		case 3:
			printf("Enter two string=>");
			scanf("%s",&str1);
			scanf("%s",&str2);
			if(STRCMP(str2,str1))
				printf("string is equal");
			else
				printf("String is not equal");
			break;
		case 4:
			printf("Enter two string=>");
			scanf("%s",str1);
			scanf("%s",str2);
			STRCAT(str3,str2,str1);
			puts(str3);
			break;
		case 5:
			printf("Enter the string=>");
			scanf("%s",str1);
			STRREV(str1);
			printf("Reverse stringis=>");
			puts(str1);
			break;
		default:
			goto end;
	}
	goto re;
end:
getch();
}
int STRLEN(char *s)
{
	int i=0;
	while(*s!=NULL)
	{
		i++;
		s++;
	}
	return i;
}
int STRCPY(char *s2,char *s1)
{
	while(*s1!=NULL)
	{
		*s2=*s1;
		s2++;
		s1++;
	}
	*s2=NULL;
	return 1;
}
int STRCMP(char *s2,char *s1)
{
	int i=0,len1,len2;
	len1=strlen(s1);
	len2=strlen(s2);
	if(len1==len2)
	{
		while(*s2==*s1 && *s2 != NULL && *s1!=NULL)
		{
			i++;
			s1++;
			s2++;
		}
		if(i==len1)
			return 1;
		else
			return 0;
	}
	else
	{
		return 0;
	}
}
int STRREV(char *s)
{
	int len;
	char *s1;
	char *ptr;
	len=strlen(s);
	s1=(char *)malloc(sizeof(char));
	strcpy(s1,s);
	ptr=s1+len-1;
	while(*s!=NULL)
	{
		*s=*ptr;
		ptr--;
		s++;
		s1++;
	}
	*s=NULL;
	return 1;
}
int STRCAT(char *s3,char *s2,char *s1)
{
	while(*s1!=NULL)
	{
		*s3=*s1;
		s3++;
		s1++;
	}
	s3++;
	while(*s2!=NULL)
	{
		*s3=*s2;
		s3++;
		s2++;
	}
	*s3=NULL;
	return 1;
}
