Error In C File Handling - c

Question

I am making a quiz program in c for a school project.I was storing question and answers in a text file.The text file contains 1 question and followed by 4 choices and a correct answer(each in a new line) and so on.The code for file handling is
#include<stdio.h>
#include<conio.h>
#include<string.h>
#include<process.h>
void main()
{
int tnum=2,mnum;
printf("Enter a file name to load the quiz from or enter dhruv.txt to load the default file\n");
printf("(For type of file and arrangement of data in it, refer to the documentation\n");
printf("WARNING: An improper quiz file may result in malfunctioning of the program.\n");
char quizfile[100];
scanf("%s",quizfile);
FILE *dj;
dj = fopen(quizfile,"r");
int test = 1;
while(dj == NULL)
{
printf("Requested file does not exist.Please enter a valid name\n");
scanf("%s",quizfile);
dj = fopen(quizfile,"r");
test++;
if(test == 5)
{
exit(0);
}
}
char line[500];
char ques[20][500],ansa[20][500],ansb[20][500],ansc[20][500],ansd[20][500],anse[20][500];
int start = 1,quesval=1,ans1=1,ans2=1,ans3=1,ans4=1,ans5=1;
while(fgets(line,sizeof line,dj) != NULL)
{
if((start%6) == 1)
{
strcpy(ques[quesval],line);
quesval++;
}
if((start%6) == 2)
{
strcpy(ansa[ans1],line);
ans1++;
}
if((start%6) == 3)
{
strcpy(ansb[ans2],line);
ans2++;
}
if((start%6) == 4)
{
strcpy(ansc[ans3],line);
ans3++;
}
if((start%6) == 0)
{
strcpy(anse[ans5],line);
ans5++;
}
if((start%6) == 5)
{
strcpy(ansd[ans4],line);
ans4++;
}
start++;
}
fclose(dj);
printf("Quiz file successfully loaded\n");
printf("/t/t WELCOME TO THE QUIZ\n\n");
printf("Every team must select one of the four correct answers to the asked questions to gain points\n");
printf("Wrong answer will not be penalized\n");
for(int k =1;k<quesval;k++)
{
int myvar;
myvar = k%tnum;
if(myvar == 0)
{
myvar = tnum;
}
printf("Question for TEAM %d\n\n",myvar);
printf("%s \n A.%s B.%s C.%s D.%s\n",ques[k],ansa[k],ansb[k],ansc[k],ansd[k]);
}
getch();
}
The problem is
if((start%6) == 0)
{
strcpy(anse[ans5],line);
ans5++;
}
The program shows File does not exist if i use this but as soon as i comment it out the program works fine.I don't know what the error is.Please do help
EDIT:My text file looks like:
Who is the owner
dhruv
jain
kalio
polika
dhruv
who is his friend
sarika
katrina
jen
aarushi
aarushi
where is he
home
office
college
toilet
office
where will he go
home
office
college
toilet
home
EDIT
I am using Turbo c++ in windows 7 using DOSBOX..The script is updated above

Answer 1

It's difficult to say without seeing your input file, but I suspect that your array declarations are backwards. For example, you have:
char ques[500][20];
This declares an array of 500 elements, where each element can be up to 20 characters. You probably want:
char ques[20][500];
This declares an array of 20 elements, where each element can be up to 500 characters.
If your input file contains lines longer than 20 characters, then your current code is likely overwriting your arrays.

Answer 2

There are several problems here but your immediate problem is this:
strcpy(anse[ans5],line);
(And all the other strcpy calls like it.)
You are copying line to the array beginning at anse[1][0]. If line contains more than 20 characters, it will overwrite memory past the end of anse. For example, if line contains 25 characters, you'll be putting it in anse[1][0] through anse[1][24]. Unfortunately anse[1][24] does not exist because anse is only 20 characters long. If any question exceeds 20 characters, you'll be corrupting memory and possibly causing a crash. Let me guess: Question 5 is longer than 19 characters, right?
In short, you have your rows and columns mixed up in your declarations. I think you wanted to allow 20 questions of 500 characters each, but you're actually allowing 500 questions of 20 characters each.
Next problem: In C, arrays are zero-based, not one-based. The first string in ques, for example, is ques[0], not ques[1].
To simplify this, think of two-dimensional arrays as a table composed of rows and columns. For example, declare a 3x4 array named foo:
char foo[3][4];
Picture it like this:
0 1 2 3
0 . . . .
1 . . . .
2 . . . .
What I have is an array of three character strings, each 4 characters long. The first string in my array is at foo[0]. The first character of the first string is at foo[0][0]. The second character is at foo[0][1], the second character of the third string is foo[2][1], and so on.
To solve this, your declarations should look like this:
char ques[20][500],ansa[20][500],ansb[20][500],ansc[20][500],ansd[20][500],anse[20][500];
int start = 1,quesval=0,ans1=0,ans2=0,ans3=0,ans4=0,ans5=0;
When you get it working, you should then ask yourself why you're testing the value of start six times each pass through the loop when it only changes once. There's a much better solution available here. Consider a three-dimensional array like this:
char answers[20][500][5];
That gives you 20 questions with 5 answers each.