How to give incremented numbers when printing data in file?

Question

In this code, I am having a problem but don't know how to solve it. I need to print the result in file with incremented numbers. I used line++ but it'll only work in the loop and I want that if someone printed something then printing again should require the line number to increment.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define STRING_LEN 200

int main(){
  FILE * fp1 = fopen("file.csv", "a");
  char string[STRING_LEN];
  int line = 1;

  printf("Enter the string: ");
  fgets(string, sizeof(string), stdin);

  fprintf(fp1, "%d,%s\n", line++, string);

  return 0;
}

Answer 1

Looks like you need something like that:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define STRING_LEN 200

int main(){
  char string[STRING_LEN];
  int line;
  FILE * fp1 = fopen("file.csv", "a+r");

  fscanf(fp1, "%d,%s\n", &line, string);
  printf("Enter the string: ");
  fgets(string, sizeof(string), stdin);
  fprintf(fp1, "%d,%s", ++line, string);
  
  fclose(fp1);
  return 0;
}

First, we read line from file, parse it and get line value, then write back incremented value. And do not forget to close file.