C program to write 5 lines to a file then print the lines except the second line

Question

This will read 5 lines into a file from stdin, then print all the lines except the second one.

I used an array because I'm not sure how to do dynamic memory allocation.

#include <stdio.h>
#include <stdlib.h>
#define MAX_SIZE 1024

void write_to_file(const char *s);
void print_file(const char *s);


int main(void){
    const char file_name[] = "text";
    write_to_file(file_name);
    print_file(file_name);

    return 0;
}

void write_to_file(const char *s){
    FILE *in_file;
    if((in_file = fopen(s, "w")) == NULL){
        perror(s);
        exit(EXIT_FAILURE);
    }

    char buffer[MAX_SIZE];
    for(int i = 0; i < 5; ++i){
        fgets(buffer, sizeof(buffer), stdin);
        fputs(buffer, in_file);
    }

    fclose(in_file);
}

void print_file(const char *s){
    FILE *in_file;
    if((in_file = fopen(s, "r")) == NULL){
        perror(s);
        exit(EXIT_FAILURE);
    }
    int c;
    int flag = 0;
    while((c = fgetc(in_file)) != EOF){
        printf("%c", c);
        if((flag == 0) && (c == '\n')){
            while((c = fgetc(in_file)) != '\n'){
                /*skip the second line*/
            }
            flag = 1;
        }
    }
}

Answer 1

You have the right idea in write_to_file(), but print_file() is awkward.

There is no need to work a character at a time in print_file(). You can read a line at a time using fgets(buffer, sizeof(buffer), in_file).

Avoid flag variables. Here, you could use a for loop to track the line number instead.

char buffer[MAX_SIZE];
for (int i = 0; fgets(buffer, sizeof(buffer), in_file) != EOF; ++i) {
    if (i != 1) puts(buffer);
}

Answer 2

Insure code easily reflects the "contract"

C program to write 5 lines to a file then print the lines except the second line

Given the above as the coding goal, consider it important that on code review (what this site does), it should be easily discernible that the goals are met.

I did not see that easy discernment in OP's code especially with the "except the second line" requirement.

Improved example:

#define WRITE_LINE_COUNT 5
#define PRINT_LINE_EXCEPT 2

....
// for(int i = 0; i < 5; ++i){
for(int i = 0; i < WRITE_LINE_COUNT; ++i){
    fgets(buffer, sizeof buffer, stdin);
    fputs(buffer, in_file);
}

...
unsigned long line = 1;
while((c = fgetc(in_file)) != EOF){
  if (line != PRINT_LINE_EXCEPT) {
    printf("%c", c);
  }
  if (c == '\n') line++;
}

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Also best to check the results of fgets() and fgetc() against NULL and EOF, respectively.