C Programming Occurrences of an Integers in an Text File - c

Question

Problem: Write a program that reads all integers that are in the range
of 0 to 100, inclusive from an input file named: a.txt and counts how
many occurrences of each are in the file. After all input has been
processed, display all the values with the number of occurrences that
were in are in the input file.
Note: The program ignores any number less than 0 or greater than 100.
Note: Do not display zero if a number is not in the file. Hints: An
array of size 101 is good enough. A number in the file plays the role
of an index.
For example: Suppose the content of the file: a.txt is as follows:
99 2 99
3
-12 80 12 33
3 99 100 1234 84
The display output is:
2 has occurred: 1 times,
3 has occurred: 2 times,
12 has occurred: 1 times,
33 has occurred: 1 times,
80 has occurred: 1 times,
84 has occurred: 1 times,
99 has occurred: 3 times,
100 has occurred: 1 times
Here is the code that I have right now:
#include <stdio.h>
#include <stdlib.h>
int main(){
FILE *inFile;
int count = 1, num[101];
inFile = fopen("a.txt", "r");
for(int i = 1; i <= 100; i++) {
fscanf(inFile, "%d", &num[i]);
}
for(int i = 1; i <= 100; i++){
if(num[i] == i) {
printf("%i has occurred: %d times\n", i, count);
count++;
}
}
fclose(inFile);
}
Output:
2 has occured: 1 times
Hello, I'm trying to do this assignment for my C Programming class due Sunday at midnight, but I'm having trouble trying to print all of the numbers from the array with their occurrences. In my code, I first declared int count to increase the number of occurrences if the number is found more than once in the text file and created an array size of 101. Then, I used a for loop to read the text file and store all the numbers from 1-100 into the array. The second for loop, followed by an if statement is to compare the numbers from the array. Even though this is a test program, we are supposed to be able to do this with all data values. Hope this is a good enough explanation, thank you.

Answer 1

You are close.
Instead of reading each value into num, You want to use your num array to keep the count of each number seen in the file.
int main() {
FILE* inFile;
int value = 0;
int result = 0;
int num[101] = { 0 }; // zero-init this array
inFile = fopen("a.txt", "r");
if (inFile == NULL) {
printf("unable to open file\n");
return -1;
}
result = fscanf(inFile, "%d", &value);
while (result == 1) {
printf("Just read: %d\n", value);
if ((value >= 0) && (value <= 100)) {
num[value] = num[value] + 1; // num[value]++
}
result = fscanf(inFile, "%d", &value);
}
for (int i = 0; i <= 100; i++) {
if (num[i] > 0) {
printf("%i has occurred: %d times\n", i, num[i]);
}
}
fclose(inFile);
}

Answer 2

In addition to the good answer by #selbie, from my answer to your earlier question How do I get the counter to work..., you can apply the same principals to filling a Frequency Array here. In this case you simply use n as an index instead of a counter.
For example with your index n and your array num declared (and initialized all zero), you would simply read all integers in the file and check if the value n was between 0 <= n <= 100 and if so , update the value at the index n in your num array by one, e.g. num[n]++;. You could do it like:
int n = 0; /* index */
int num[NELEM] = {0}; /* array */
...
while (fscanf(myFile, "%d", &n) == 1) /* read each int */
if (0 <= n && n <= 100) /* if 0 <= n <= 100 */
num[n]++; /* increment value at index */
Then for your output, you just handle your special check on num[0] to determine whether to output that index, and then loop from 1-NELEM outputting the frequency of occurrence of each value, e.g.
if (num[0]) /* check if 0 found, output if so */
printf ("num[%3d] occurred %3d times\n", 0, num[0]);
for (int i = 1; i < NELEM; i++) /* output counts for 1-100 */
printf ("num[%3d] occurred %3d times\n", i, num[i]);
The complete example could be:
#include <stdio.h>
#define NELEM 101 /* if you need a constant, #define one (or more) */
int main(int argc, char **argv) {
int n = 0; /* index */
int num[NELEM] = {0}; /* array */
/* read filename from 1st argument (stdin by default) */
FILE *myFile = argc > 1 ? fopen (argv[1], "r") : stdin;
if (!myFile) { /* validate myfile is open for reading */
perror ("fopen-myfile");
return 1;
}
while (fscanf(myFile, "%d", &n) == 1) /* read each int */
if (0 <= n && n <= 100) /* if 0 <= n <= 100 */
num[n]++; /* increment value at index */
if (myFile != stdin) /* close file if not stdin */
fclose (myFile);
if (num[0]) /* check if 0 found, output if so */
printf ("num[%3d] occurred %3d times\n", 0, num[0]);
for (int i = 1; i < NELEM; i++) /* output counts for 1-100 */
printf ("num[%3d] occurred %3d times\n", i, num[i]);
}
Example Use/Output
With 500 random integers in a file, you would get output similar to:
$ ./bin/fscanffreq dat/500_rand_0-100.txt
num[ 0] occurred 3 times
num[ 1] occurred 8 times
num[ 2] occurred 7 times
num[ 3] occurred 2 times
num[ 4] occurred 1 times
num[ 5] occurred 4 times
num[ 6] occurred 3 times
num[ 7] occurred 5 times
num[ 8] occurred 6 times
num[ 9] occurred 4 times
num[ 10] occurred 6 times
...
num[ 95] occurred 6 times
num[ 96] occurred 4 times
num[ 97] occurred 6 times
num[ 98] occurred 2 times
num[ 99] occurred 5 times
num[100] occurred 6 times
(note: if num[0] was 0, it would not be displayed)
Look things over and let me know if you have further questions.