my_strrev(char str[Max]){
    int i; // pointing to base adress
    int l; //pointing to last address strlen(str) -1th position
    char temp;
    for(i=0,l=strlen(str)-1;i<=l; i++ ,j--)
    {
      temp=str[i];
      str[i]=str[l];
      str[l]=temp;
    }
    return str;
}

char * rev(char * str){
 int temp;  
 for(int j=0;str[j];j++);     
 for(int i=0;i<j;i++,j--){
        temp=str[i];
        str[i]=str[j];
        str[j]=temp;
    } 
 return str;
}

#include<iostream.h>
#include<conio.h>
#include<string.h>
#include<stdio.h>
int main()
{
int i=0,l,l1;
char str[100];
cout<<"enter string:";
gets(str);
while(str[i])
i++;
l=i;
for(i=0;i<=(l-1)/2;i++)   //n/2 steps!!no extra memory
{
char t=str[i];
str[i]=str[l-i-1];
str[l-i-1]=t;
}
str[l]=0;
cout<<"\n\nreversed string is:"<<str;
getch();
return 0;
}

char * rev_string (char * str)
{
char temp;
int i , j;
for (i = 0 ; str[i]!= NULL ; i++);

for(j = 0 ; j < i ; j++ , i--)
{
      temp = str[j];
      str[j] = str[i];
      str[i] = temp;
}

return str;
}

the above is slightly wrong
this is the corrected one..

char * rev_string (char * str)
{
char temp;
int i , j;
for (i = 0 ; str[i]!= '\0' ; i++);

for(j = 0 ; j < i ; j++ , i--)
{
      temp = str[j];
      str[j] = str[i];
      str[i] = temp;
}

return str;
}

#include<stdio.h>

void reverse(char *);

void main()
{
	char str[]="Hello";

	reverse(str);
	printf("Reverse String is %s",str);
	
}

void reverse(char *p)
{

	char *q=p;
	while(*++q!='\0');
	q--;

	while(p<q)
	{
		*p=*p+*q;
		*q=*p-*q;
		*p=*p-*q;
		p++;
		q--;
	}

}

char * rev_string (char * str)
{
char temp;
int i , j;
for (i = 0 ; str[i]!= '\0' ; i++);
i--;

for(j = 0 ; j < i ; j++ , i--)
{
      temp = str[j];
      str[j] = str[i];
      str[i] = temp;
}

return str;
}

#include<muthu.h>
main()
 {
   printf("\nthe reverse string is:",reversemuthu(s1);
 }

output:
 original string is: muthu
 the reverse string is: uthum
   
Thanks and recgards:
   prof.muthu ph:9962940220
 you can call me any time any where...!