Memory can't be read when shortest function is run - c

Question

I had a bunch of problems with this program but looks like this might be inches away from completion and I was hoping someone could tell me what the hell's wrong with the blasted thing!
#include <stdio.h>
#include <string.h>
#define SIZE_OF_STRING 21
void displayMenu(void);
void readArray(char [][SIZE_OF_STRING], int);
void printArray(char [][SIZE_OF_STRING], int);
int shortestArray(char [][SIZE_OF_STRING], int);
int smallestArray(char [][SIZE_OF_STRING], int);
void sortArray(char [][SIZE_OF_STRING], int);
int main(void)
{
int position, n = 0; /* all local to main */
char select[10]; /* select is a string */
char array[1000][SIZE_OF_STRING];
displayMenu();
scanf("%s", select); /* read first selection */
while (strcmp(select, "exit") != 0) /* while not exit */
{
if (strcmp(select, "read") == 0)
{
printf("How many names?");
scanf("%d", &n);
n++;
printf("Enter %d names", n - 1);
readArray(array, n);
}
else if (strcmp(select, "display") == 0)
{
printArray(array, n);
}
else if (strcmp(select, "shortest") == 0)
{
position = shortestArray(array, n);
printf("Shortest name is %s in position %d\n", array[position], position + 1);
}
else if (strcmp(select, "lowest") == 0)
{
position = smallestArray(array, n);
printf("Lowest name is %s in position %d\n",
array[position], position + 1);
}
else if (strcmp(select, "sort") == 0)
{
sortArray(array, n);
}
else
{
printf("INVALID SELECTION");
}
displayMenu();
scanf("%s", select); /* read next selection */
} /* end while */
}/* end main */
void displayMenu(void)
{
puts("Menu selection");
puts("Enter read to read names");
puts("Enter display to display names");
puts("Enter shortest for shortest name");
puts("Enter lowest for lowest names");
puts("Enter sort to sort names");
puts("Enter exit to exit\n");
}
void readArray(char a[][SIZE_OF_STRING], int n)
{
int i;
printf("\ntype one string per line\n");
for (i=0; i<n; i++)
{
gets(a[i]);
}
}
void printArray(char a[][SIZE_OF_STRING], int n)
{
int i;
printf("\ntype one string per line\n");
for (i=0; i<n; i++)
{
puts(a[i]);
}
}
int shortestArray(char a[][SIZE_OF_STRING], int n)
{
int i;
int chag = 0;
int position;
while (a[i] != '\0')
{
if (strlen(a[i]) < strlen(a[i-1]))
{
position = i;
chag = 1;
}
else
{
if (chag = 0)
{
position = 1;
}
else
{
printf("");
}
}
}
return position;
}
int smallestArray(char a[][SIZE_OF_STRING], int n)
{
puts("Not yet implemented\n");
return 0;
}
void sortArray(char a[][SIZE_OF_STRING], int n)
{
puts("Not yet implemented\n");
}
only worried about "shortest" function at the moment all others run okay.
I also know there are better ways of doing the search but I keep getting "declaration creates integer from pointer without cast" errors when I change to a more standard search with a default smallest etc.
chag is to say whether or not number one in a[] is the smallest as it never gets checked, going to change this as soon as I get it working as I can see a more effective way of doing it.
[edit]
My bad, the error that appears is an application error when "smallest" is selected.
the following appears
"the instruction at "0x77c478c0" referenced memory at "0xd2fd82e0". the memory could not be "read".
ok to terminate program, cancel to debug.
changed the shortest function to the following and still get a similar memory message;
int shortestArray(char a[][SIZE_OF_STRING], int n)
{
int i = 1;
int position = 1;
while (a[i] != '\0')
{
if (strlen(a[i + 1]) < strlen(a[i]))
{
position = i + 1;
i++;
}
else
{
i++;
}
}
return position;
}

Answer 1

There's a clbuttic typo in shortestArray():
if (chag = 0) {
position = 1;
}
// ...
This will always evaluate to false, so the else block is run.
Here, zero is assigned to chag which makes the expression evaluate to zero (false). Use the comparision operator == instead. You might want to crank up warning levels as I'm sure, any C compiler has an appropriate message for this.

Answer 2

One big and obvious problem is that in the function you use the variable i without initializing it.
Another problem is this expression: strlen(a[i-1]). If i is 0 then this will access memory before the array.

Answer 3

In addition to the other answers so far:
You don't increment i either.
If I imagine all the trivial fixes applied (correct iteration, comparison instead of assignment in the condition), the function is going to return position of last local minimum of length. I.e. having list of strings like
"a", "bbbb", "ccc", "dd"
it will return 3, but shortest string is at position 0!
You do remember array indices in C start from 0, right (in position = 1)?

Answer 4

you have to know the number of strings entered in the array to avoid unknown behavior.
a way to do this : in main, just after declaration of array, put :
strcpy(array[0], ""); // to indicate that the array is empty.
in the end of readArray() :
strcpy(a[n] , ""); // there is n strings written bythe user (a[0] to a[n-1]).
and finally :
in shortestArray(), the stop condition of the loop must be changed to :
while (strcmp(a[i],"") != 0 ) //a[i] == '\0' is not correct because a[i] is string and '\0' is char.
here is the entire code with the changes i made :
#include <stdio.h>
#include <string.h>
#define SIZE_OF_STRING 21
#define SIZE_OF_ARRAY 1000
void displayMenu(void);
void readArray(char [][SIZE_OF_STRING], int);
void printArray(char [][SIZE_OF_STRING]);
int shortestArray(char [][SIZE_OF_STRING]);
int smallestArray(char [][SIZE_OF_STRING], int);
void sortArray(char [][SIZE_OF_STRING], int);
int main(void)
{
int position, n = 0; /* all local to main */
char select[10]; /* select is a string */
char array[SIZE_OF_ARRAY][SIZE_OF_STRING]; //change here !
strcpy(array[0] , ""); //instruction added : means array is empty
displayMenu();
scanf("%s", select); /* read first selection */
while (strcmp(select, "exit") != 0) /* while not exit */
{
if (strcmp(select, "read") == 0)
{
printf("How many names?");
scanf("%d", &n);
while (n >= SIZE_OF_ARRAY)
{
printf("the number you entered is bigger than the maximum number of strings, please enter a number smaller than %d\n", SIZE_OF_ARRAY);
}
printf("Enter %d names", n);
readArray(array, n);
}
else if (strcmp(select, "display") == 0)
{
printArray(array);
}
else if (strcmp(select, "shortest") == 0)
{
position = shortestArray(array);
if (position == -1)
printf("there is no string entered !\n");
else
printf("Shortest name is %s in position %d\n", array[position-1], position );
}
else if (strcmp(select, "lowest") == 0)
{
position = smallestArray(array, n);
printf("Lowest name is %s in position %d\n",
array[position], position + 1);
}
else if (strcmp(select, "sort") == 0)
{
sortArray(array, n);
}
else
{
printf("INVALID SELECTION");
}
displayMenu();
scanf("%s", select); /* read next selection */
} /* end while */
}/* end main */
void displayMenu(void)
{
puts("Menu selection");
puts("Enter read to read names");
puts("Enter display to display names");
puts("Enter shortest for shortest name");
puts("Enter lowest for lowest names");
puts("Enter sort to sort names");
puts("Enter exit to exit\n");
}
void readArray(char a[][SIZE_OF_STRING], int n)
{
int i;
printf("\ntype one string per line\n");
for (i=0; i<n; i++)
{
scanf("%s",a[i]);
}
strcpy(a[n] , "");
}
void printArray(char a[][SIZE_OF_STRING])
{
int i;
for (i=0; i< SIZE_OF_ARRAY; i++)
{
if (strcmp(a[i] , "") == 0) // a[i-1] is last string entered
break; // this avoid printing non initialized string causing unknown behaviour.
printf("%s\n",a[i]);
}
}
int shortestArray(char a[][SIZE_OF_STRING])
{
int i = 0;
int position = 1;
if(strcmp (a[i] , "\0") == 0)
return position = -1; // there no string entered.
while (strcmp (a[i+1] , "\0") != 0)
{
if (strlen(a[i+1]) < strlen(a[i]))
{
position = i+2 ;
i++;
}
else
{
i++;
}
}
return position;
}
int smallestArray(char a[][SIZE_OF_STRING], int n)
{
puts("Not yet implemented\n");
return 0;
}
void sortArray(char a[][SIZE_OF_STRING], int n)
{
puts("Not yet implemented\n");
}