Seg. fault read line-by-line - c

Question

I am trying to calculate the mode or the integer that appears the most for each line.
I get an print two values and then segmentation fault.
for (i = 0; i < count; i++) {
if (array[i]) {
int i, j, k, cnt = 1, p, big;
int b[MAX_NUM] = {0};
printf("count:%d\n", count);
for (i = 1; i <= array[i]; i++) {
for (j = i + 1; j <= array[i]; j++) {
if (array[i] == array[j])
printf("cnt:%d\n", cnt);
cnt++;
}
printf("cnt2:%d\n", cnt);
b[k] = cnt;
k++;
cnt = 1;
}
big = b[k];
p = 1;
for (i = 2; i <= array[i]; i++) {
if (big < b[i]) {
big = b[i];
p = i;
}
}
printf("The element that occurs offen is %d\n", array[p]);
printf("And it has occurred %d times\n", b[p]);
}
}
}
}
}
return 0;
}
EDIT:
See the look here in my code. The values that are printed are the numbers on each line of the file followed by a blank line like this:
1
2
3
4
5
6
5
4
5
14
62
48
14
1
3
5
7
9
123
456
789
1234
5678
34
34
34
34
34
1
1
2
2
2
2
2
3
3
4
4
4
4
5
5
6
7
7
7
1
1
Integers: 9
.....

Answer 1

You redefine i and p in an inner scope where they shadow current definitions. This is obviously unintentional as the for expression looks quite wrong:
if (array[i]) {
int i, j, k=1, cnt = 1, p, big;
// ^
// Redefinition of i.
// You should use a different name for the loop index below
// Same remark for p, it is safer to not redefine local variables
// in inner scopes. Any { starting a block creates a new scope
// in which variables can be defined, or in this case redefined.
...
for (i = 1; i <= array[i]; i++) {
...
for (i = 2; i <= array[i]; i++) {
...
In the same area of the code, you use k without a prior initialization.
The code to compute maximum occurrences can be put into a separate function and simplified this way:
#include <stdio.h>
// get the number of ocurrences of val in array a of size n
int get_number_of_occurrences(int a[], int n, int val) {
int cnt = 0, i;
for (i = 0; i < n; i++) {
if (a[i] == val)
cnt++;
}
return cnt;
}
// return the index for the number that occurs the most
int get_max_occurrence_index(int a[], int n) {
int p = 0, cnt, max = 0, i;
for (i = 0; i < n; i++) {
cnt = get_number_of_occurrences(a, n, a[i]);
if (max < cnt) {
max = cnt;
p = i;
}
}
return p;
}
int main() {
int i, n, a[20], max;
printf("Enter the maximum number of elements\n");
scanf("%d", &n);
printf("Enter the elements\n");
for (i = 0; i < n; i++) {
scanf("%d", &a[i]);
}
i = get_max_occurrence_index(a, n);
max = get_number_of_occurrences(a, n, a[i]);
printf("The element that occurs most oftenly is %d\n", a[i]);
printf("And it has occurred %d times\n", max);
return 0;
}
If you want to use this logic in your original program, you should use it for each line as you read the file instead of at the end where it only applies to the last line. The line parsing code is incorrect too: you take the first digit's ASCII value as the value instead of parsing it with strtol().
Here is a corrected version:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#define MAX_NUM 1000
#define MAX_LINE_LEN 2048
#define N 100
void fatal(const char *msg) {
printf("%s\n", msg);
exit(1);
}
int main(int argc, char *argv[]) {
FILE *fp;
char filename[100];
char line[MAX_LINE_LEN];
char *p;
int array[MAX_NUM];
int index, count, max;
printf("Please enter the file name: \n");
if (scanf("%99s", filename) != 1) {
fatal("Error in entering file.");
}
if ((fp = fopen(filename, "r")) == NULL) {
fatal("Unable to open the file.");
}
while ((p = fgets(line, MAX_LINE_LEN, fp)) != NULL) {
/* skip white space */
p += strspn(p, " \t\n");
if (*p == '#' || *p == '\0') {
/* ignore comment and blank lines */
continue;
}
/* scan and convert the numbers */
for (count = 0; *p != '\0'; ) {
if (isdigit((unsigned char)*p)) {
array[count++] = strtol(p, &p, 10);
printf("%d\n", array[count]);
} else {
/* skip to next space or end of string */
p += strcspn(p, " \t\n");
}
/* skip white space after the number */
p += strspn(p, " \t\n");
}
index = get_max_occurrence_index(array, count);
max = get_number_of_occurrences(array, count, array[index]);
printf("The element that occurs most often is %d\n", array[index]);
printf("And it has occurred %d times\n", max);
}
fclose(fp);
return 0;
}

Answer 2

Maybe i just can not see through your code, but at no point do i see you loading the actual numbers from your file into any variable or array to work with.
You are loading a line with while ((p = fgets(line, MAX_LINE_LEN, fp)) != NULL) {
Inside that loop, you are breaking this line into tokens to count how many numbers you have.
As far as i can see, array[count]++; is used to count how many numbers are in each line. Using the index as the line number.
You should start by thinking about how to get your data into a usable format
You can start trying to load the values into a 2 dimensional array.
Using the first dimension for the line number and the second for the values.
If you don't understand your code well enough, you should start with more comments
What do you use your difines and variables for.
#define MAX_NUM 1000 //maximum number of lines
int array[MAX_NUM] = {0}; //index refers to line number of file. used to count numbers in each line.
// read file line by line, split every line into tokens to count amount of numbers
while ((p = fgets(line, MAX_LINE_LEN, fp)) != NULL) {
if (count >= MAX_NUM) {
fatal("Array error");
}
if (line[0] != '#') {
p = strtok(line, " ");
while (p != NULL) {
if (isdigit(*p)) {
array[count]++;
}
p = strtok(NULL, " ");
}
}
count++;
//printf("COUNT:%D\n", count);
}
Choosing good variable names in addition would be even better
#define MAX_NUM 1000 -> #define MAX_LINE_NUM 1000
I have no idea about what your variables int i, j, k, cnt = 1, p, big; do.
Give them better names and or comment them. Will not only help you, but your helpers that need to understand what you intend to do with them.
First i thought you needed help with the algorithm for the mode so i wrote this first:
Using very basic stuff to keep it as simple as possible.
Would be cleaner to put it into functions if you know how.
Did not use functions since it seems you do not know completely how to work with them (you should look into that)
This algorithm is doing the following:
Take the first number in the array
Run through the array and everytime you find that number, you increase a counter
Save the number and the count as highest and highestCnt
Repeat with every number in the array and overwrite highest and highestCnt whenever count > highestCnt
When there are multiple number with the highest occurrence it will only remember the number that was counted first. If you want to return all numbers with the highest occurrence, the coude would need to be changed.
Could do something like checking if count == highestCnt and then set something so you know there is no single number with the highest count until you find one with an even higher count.
#include<stdio.h>
#define sizea 100
int main(void) {
int array[sizea] = { 1,3,6,8,3,6,7,4,6,9,0,3,5,12,65,3,76,5,3,54,
1,3,6,89,3,6,7,4,6,9,0,4,5,12,65,3,76,5,3,54,
1,9,6,8,3,45,7,4,6,9,0,89,5,12,65,3,76,5,3,54,
6,3,6,8,3,6,7,4,6,9,0,23,5,12,65,3,76,5,3,54,
1,3,6,90,3,6,7,4,6,9,0,5,5,12,65,3,76,5,3,54 };
int number;
int count = 1;
int highest = 1;
int highestCnt = 1;
int end = sizea - 1; //end defines at what element in the array the loop will end
int j; //j is used to load a number that will be count
int i; //i is used run through the array and compare every number the the one that is being count
for (j = 0; j <= end; j++) {
number = array[j]; // load a number to count
count = 1; // start counting at 1
for (i = j+1; i <= end; i++) {
// if we find the same number again, we increase the counter
// then we load the last element into the current array position
// then we change decrement "end" by 1
// this is like throwing out all the numbers we allready count
// using while instead of if so it will check the last element that was moved to current position as well
// check for i <= end so it doesnt count twice when the last element equals our number
while (array[i] == number && i <= end) {
count++;
array[i] = array[end];
end--;
}
}
// if the count of the number is highers the the previus highest, it's obviously our new highest count.
if (count > highestCnt) {
highest = number;
highestCnt = count;
}
}
printf("number: %i, count: %i", highest, highestCnt);
}