Exercise 1-19 from The C Programming Language by Brian W. Kernighan, Dennis M. Ritchie​. "Write a function reverse(s) that reverses the character string s. Use it to write a program that reverses its input line by line" Only instead of a function I've written a small program that accepts piped in input and does it there

reverse.c

#include <stdio.h>

#define MAXLENGTH 1000

//Write a function reverse(s) that reverses the character string s. Use it to write a program that reverses its input line by line

void reverse(char s[], int lim){
	int i,j;
	j=lim-1;
	i=0;

	while(i < j){
		//XOR Swap algorithm to save space and for efficiency
		s[i] ^= s[j];
		s[j] ^= s[i];
		s[i] ^= s[j];
		++i; --j;
	}
}

int ourgetline(char s[], int lim){
	int c,i;

	for(i=0; i < lim-1 && (c=getchar()) != EOF && c != '\n'; ++i)
		s[i] = c;
	if(c == '\n'){
		s[i] = c;
		++i;
	}
	s[i] = '\0';
	return i;
}

main(){
	char in[MAXLENGTH];
	int len;

	len=0;
	while((len = ourgetline(in,MAXLENGTH)) > 0){
		reverse(in,len);	
		printf("%s", in);
	}
	

}

Usage:

$ cc reverse.c -o reverse
$ ./reverse < filetoreverse.txt > output.txt

include <stdio.h>

define MAXLENGTH 1000

//Write a function reverse(s) that reverses the character string s. Use it to write a program that reverses its input line by line

void reverse(char s[], int lim){
int i,j;
j=lim-1;
i=0;

while(i < j){
    //XOR Swap algorithm to save space and for efficiency
    s[i] ^= s[j];
    s[j] ^= s[i];
    s[i] ^= s[j];
    ++i; --j;
}

}

int ourgetline(char s[], int lim){
int c,i;

for(i=0; i < lim-1 && (c=getchar()) != EOF && c != '\n'; ++i)
    s[i] = c;
if(c == '\n'){
    s[i] = c;
    ++i;
}
s[i] = '\0';
return i;

}

void main(){
char in[MAXLENGTH];
int len;

len=0;
while((len = ourgetline(in,MAXLENGTH)) > 1)//replace 0 with 1 so that program can terminate
{
    reverse(in,len);    
    printf("%s", in);
}

}

#include <stdio.h>
#include <string.h>

int main(){

    char *name = "Santee" ;
    int len = strlen(name) ;
    name += len ;
    while (len--)
        printf("%c", *--name) ;
    
    return 0 ;
}