I/O: You should be able to know at least one syntax on how to open a file and then read from it and/or write/append to it. Also write data into screen (one simple command is "print") code example

Example 1: write in file in c

#include<stdio.h>
int main(){
	FILE *out=fopen("name_of_file.txt","w");
	fputs("Hello File",out);
	fclose(out);
	return 0;
}

Example 2: c program to read and write to a file

/*Program to read from file using getc() function*/
#include <stdio.h>
int main() {
 FILE *fp;
 char ch;
 /*Open file in read mode*/
 fp= fopen ('example.txt', 'r');
 while( (ch = getc(fp)) != EOF) {
  /*getc() function reads a character and its value is stored in variable 'ch' until EOF is encountered*/
  printf('%ch', ch);
 }
  fclose(fp);
  return 0;
}