How to reverse a structure in text file with C? - reverse

Question

I have an exercise and I don't know how to solve it well!
I want write a C program that give from user the information of a student and then save it to file A.txt. After that reverse the first name, last name and student number and save it to file B.txt.
For example:
john
lopez
123456
It changes to:
nhoj
zepol
654321
#include <stdio.h>
#include <stdlib.h>
#define SIZE 50
struct student {
char fname[SIZE];
char lname[SIZE];
char num[SIZE];
}st;
int main()
{
FILE *in, *out;
char ch;
int tmp=0,flag=0,i;
printf("INPUT First name: ");
scanf("%s", &st.fname);
printf("INPUT Last name: ");
scanf("%s", &st.lname);
printf("INPUT personal num: ");
scanf("%s", &st.num);
in= fopen("A.txt", "w");
fputs(st.fname, in);
fputs(st.lname, in);
fputs(st.num, in);
fclose(in);
in= fopen("A.txt", "r");
out=fopen("B.txt", "w");
fgets(st.fname, strlen(st.fname)+1,in);
strrev(st.fname);
fputs(st.fname, out);
printf("\n%s", st.fname);
fgets(st.lname, strlen(st.lname)+1, in);
strrev(st.lname);
fputs(st.lname, out);
printf("\n%s", st.lname);
fgets(st.num, strlen(st.num)+1, in);
strrev(&st.num);
fputs(st.num, out);
printf("\n%d", st.num);
fclose(in);
fclose(out);
return 0;
}

Answer 1

If you want to copy the data to a file, then you first need to put the data in some dynamic memory allocation and then after reversing the content required in dynamic memory, you need to copy it into your file.

Answer 2

this is the program to reverse the each word in given string
#include
#include
void reverse_string(char*);
void reverse_words(char*);
int main() {
char a[100];
gets(a);
reverse_words(a);
printf("%s\n", a);
return 0;
}
void reverse_words(char *s) {
char b[100], *t, *z;
int c = 0;
t = s;
while(*t) { //processing complete string
while(*t != ' ' && *t != '\0') { //extracting word from string
b[c] = *t;
t++;
c++;
}
b[c] = '\0';
c = 0;
reverse_string(b); // reverse the extracted word
z = b;
while (*z) { //copying the reversed word into original string
*s = *z;
z++;
s++;
}
while (*s == ' ') { // skipping space(s)
s++;
}
/*
* You may use if statement in place of while loop if
* you are assuming only one space between words. If condition is
* used because null terminator can also occur after a word, in
* that case we don't want to increment pointer.
* if (*s == ' ') {
* s++;
* }
*/
t = s; // pointing to next word
}
}
/*
* Function to reverse a word.
*/
void reverse_string(char *t) {
int l, c;
char *e, s;
l = strlen(t);
e = t + l - 1;
for (c = 0; c < l/2; c++) {
s = *t;
*t = *e;
*e = s;
t++;
e--;
}
}

Answer 3

Then you can try using fputc, i.e., reading char by char along with a loop to get your data line by line as 3 lines.
char *ch;
for(i=0;st.fname[i];i++)
{
ch=getc(st.fname[i]);
fputc(ch,in);
}
repeat the same even for st.lname and st.num