How can I delete extra break line when read txt in C - c

Question

I'm new in C and try to do some practice
I want to change the txt file from
Chicken
10000
Cow
20000
Duck
20
Sheep
1000
to
Chicken 10000
Cow 20000
Duck 20
Sheep 1000
then destroy the animal <50
Chicken 10000
Cow 20000
Sheep 1000
My first step:
Read the file and compose the letter to the string.
Like the first word "Chicken", will be composed of "C" "h" "i" "c" "k" "e" "n".
As following my code, when I use strcpy(str0, ""); I have changed the string array strings[0] = str0; (str0 is "Chicken" now) before strcpy(str0, "");, but when strcpy(str0, "");operate, my memory in strings[0] was also be changed.
How can I fix the problem?
This is my code:
void append(char* s, char c)
{
int len = strlen(s);
s[len] = c;
s[len+1] = '\0';
}
int main() {
char str0[256] = "";
char tmp_char;
const char *string[2];
int i, c, line_counter=0;
FILE *file;
file = fopen("cry.txt", "r");
if (file) {
while ((c=getc(file)) !=EOF) {
if (c == 10) {
line_counter++;
string[0]=str0;
strcpy(str0, "");
continue;
}
tmp_char = c;
append(str0, tmp_char);
}
fclose(file);
}
return 0;
}

Answer 1

You should divide your problem into smaller pieces and implement them independently from each other --> "divide and conquer"
Before starting programming you should think about the steps.
I would analyze the problem the following way:
open infile
open outfile
while not eof
read data set --> 2 lines
read a line -> parse animal name
read a line -> parse number
filter data set
write data set
close files
I would derive the following structures/functions from this (or use library functions - depending on the class's task):
structure
DataSet{animalName, count};
function
readLine(filehandle, bufferpointer, maxbuffersize) -> success
readDataset(bufferpointer1, bufferpointer2) -> success
(parseAnimalName(linebuffer1, buffersize, namebuffer, maxlength) -> success)
(parseAnimalCount(linebuffer, numberpinter) -> success)
filterAnimal(DataSet) -> bool
writeAnimal(filehandle, DataSet) --> success
Depending on the possibility to use libraries parse functions I would omit the functions in parentheses.
With this isolated little functionalities it should be a lot easier to implement the whole problem and also analyze where bugs occur.

Answer 2

Once you solve the problem yourself you can compare it with my solution. I commented it pretty heavily.
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define LIMIT 30
// Arbitrary max number of items
#define MAX_ITEMS 16
// Arbitrary maximum result size
#define MAX_RESULT_SIZE 256
// Output string must keep both animal name and stringified integer.
// This integer will take at most 11 characters.
// It means that in string of format "%s %d\n" the animal name
// must take at most (MAX_RESULT_SIZE - 11 - whitespace - \n - NUL) characters.
#define MAX_STR_SIZE ((MAX_RESULT_SIZE) - 14)
int main(void) {
int retcode;
const char *filename = "file.txt";
FILE *file = fopen("file.txt", "r");
if (file == NULL) {
fprintf(stderr, "Failed to open file %s: %s", filename, strerror(errno));
}
char text[MAX_STR_SIZE + 1];
int number;
int id = 0;
char results[MAX_ITEMS][MAX_RESULT_SIZE];
// Dynamically define fmt string to limit fscanf to MAX_STR_SIZE
// Format specifier "%256s" makes sure that fscanf won't read a string that is
// longer than 256 characters (remember about additional one byte for NUL character,
// output memory must have space for 257 characters).
char fmt[32];
snprintf(fmt, sizeof(fmt), "%%%zus\n", (size_t)MAX_STR_SIZE);
while(1) {
if (id >= MAX_ITEMS) break;
retcode = fscanf(file, fmt, text);
if (retcode == EOF) break;
// From fscanf manual page we know 'On success, these functions return the
// number of input items successfully matched and assigned'. If this is
// different than 1 then something went wrong with input string. Maybe
// It's different than we assumed.
if (retcode != 1) {
fprintf(stderr, "Input is not matching format specifiers");
exit(EXIT_FAILURE);
}
retcode = fscanf(file, "%d\n", &number);
if (retcode == EOF) break;
if (retcode != 1) {
fprintf(stderr, "Input is not matching format specifiers");
exit(EXIT_FAILURE);
}
// Filtering logic
if (number < LIMIT) continue;
sprintf(results[id++], "%.*s %d", MAX_STR_SIZE, text, number);
}
for(int i = 0; i < id; i++) printf("%s\n", results[i]);
fclose(file);
return 0;
}

Answer 3

your line just assigns pointer to the variable str0 into string[0]
string[0]=str0;
That is why your string[0] changes after str0 changes. They point to the same memory.
To solve this, you have to copy value from str0 into string[0]