Question

Create a C Program that reads a file and replaces every other letter with an asterisk. The first integer 'num' is the number of lines.

Include an "Error" Message and exit the program if:
   The wrong name for the input/output file is given
   The input/output file can not be opened

input.txt
7
Never
Have
We
Ever
Played
A
Game

output.txt
7
N*v*r
*a*e
W*
*v*r
*l*y*d
*
G*m*

Answer 1

If you have any doubts, please give me comment...

#include<stdio.h>

int main(){

char in_fname[50], out_fname[50], line[100];

int num;

printf("Enter input filename: ");

scanf("%s", in_fname);

FILE *fin = fopen(in_fname, "r");

if(fin==NULL){

printf("Error: Unable to open input file!\n");

return -1;

}

printf("Enter output filename: ");

scanf("%s", out_fname);

FILE *fout = fopen(out_fname, "w");

if(fout==NULL){

printf("Error: Unable to open output file!\n");

return -1;

}

fscanf(fin, "%d", &num);

int j = 0, k;

for(int i=0; i<num; i++){

fscanf(fin, "\n%[^\n]s", line);

k = 0;

while(line[k]!='\0'){

if(j%2!=0)

line[k] = '*';

k++;

j++;

}

fprintf(fout, "%s\n", line);

}

fclose(fout);

fclose(fin);

return 0;

}