1-19

Quest: page 31

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Write a function reverse(s) that reverses the caracter string s. Use it to write a program taht reverses its input a line at a time.

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reverse each line programm

• it prints each line and then the reversed version
• i used a tmp var to save the value of the swapped target.
• i used two pointer i and j moving i from left to right and j from right to left.

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>

#define MAX 1000

int gl(char line[], int maxline);
void cp(char to[], char from[]);
void trimTrailing(char line[], int len);
void reverse(char s[], int len);

int main() {
  int len;
  char line[MAX];
  while ((len = gl(line, MAX)) > 0) {
    if (line[0] == '\n') {
      continue;
    }
    printf("%s", line);
    reverse(line, len);
    printf("%s", line);
  }
  return EXIT_SUCCESS;
}

void reverse(char s[], int len) {
  int i;
  int j = len - 2;
  char tmp;
  for (i = 0; i < j;) {
    tmp = s[i];
    s[i] = s[j];
    s[j] = tmp;
    j--;
    i++;
  }
}

void trimTrailing(char line[], int len) {
  int i;
  for (i = len - 2; isblank(line[i]); i--)
    ;
  line[++i] = '\0';
}

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

void cp(char to[], char from[]) {
  int i;
  i = 0;
  while ((to[i] = from[i]) != '\n') {
    ++i;
  }
}