How to group lines of data using fscanf - c

Question

I've been having trouble with a program. The first number in the file is the number of "sets" the program needs to run. For every set, I need it to read the next 6 integers, split into two groups. For example, with this data set:
{3, 4, 6, 8, 5, 5, 7, 9, 8, 7, 2, 4, 5, 6, 9, 1, 5, 7, 6}
The program should run 3 sets. In set one, it needs to read the next three integers in one group, then the next three integers in the other group, then move to the next set. So
Set 1:
[4, 6, 8] = 18
[5, 5, 7] = 17
Set 2:
[9, 8, 7] = 24
[2, 4, 5] = 11
Set 3:
[6, 9, 1] = 16
[5, 7, 6] = 18
I'm honestly not sure where to start. I've managed to get it to read the first number as the set number, but I'm not sure how to group the integers the way I need it to.
Here's the code so far:
int main(){
int set_number, set_total, points_1, points_2;
int point_total_1 = 0, point_total_2 = 0;
FILE * ifp;
char input_name[50] = "";
printf("Please enter file input name for scores.\n\n");
scanf("%s", &input_name);
ifp = fopen(input_name, "r");
fscanf(ifp, "%d", &set_total);
FILE * ofp = fopen("ninja_scores_output.txt", "w");
for(set_number = 1; set_number <= set_total; set_number++){
fprintf(ofp,"Set #%d:\n", set_number);
fprintf(ofp,"Student 1: %d points.\n\n", points_1);
fprintf(ofp,"Student 2: %d points.\n\n", points_2);
point_total_1 += points_1;
point_total_2 += points_2;
}
fprintf(ofp,"Final Scores:\n"
"Student 1: %d total points.\n\n", point_total_1);
fprintf(ofp,"Student 2: %d total points.\n\n", point_total_2);
if(point_total_1 > point_total_2){
fprintf(ofp, "Student 1 will move onto the next round!");
}
else if(point_total_2 > point_total_1){
fprintf(ofp, "Student 2 will move onto the next round!");
}
fclose(ofp);
fclose(ifp);
return 0;
}
EDIT:
After some tinkering, I managed to get it to read the lines properly, but something's still going wrong. How do I get it to continue down the lines after it finishes it's first loop? In the test file, the values are: {3, 3, 3, 19, 16, 8, 9, 15, 1, 14, 12, 13, 1, 7, 8, 9, 6, 6, 5} (All on new lines). When I run the program, it runs three sets, but in the first set, it's listing student 1 as earning 65 points, while student 2 earned 15 points. In subsequent sets, student 1's score only increases by 6 and student 2 only increases by 15. I'm not sure how to fix it.
Here's the new code:
int main(){
int set_number, set_total, point_val, points_1, points_2;
int point_total_1 = 0, point_total_2 = 0;
FILE * ifp;
char input_name[50] = "";
printf("Please enter file input name for scores.\n\n");
scanf("%s", &input_name);
ifp = fopen(input_name, "r");
FILE * ofp = fopen("ninja_scores_output.txt", "w");
fscanf(ifp, "%d", &set_total);
int current_throw;
int throw_value;
for(set_number = 1; set_number <= set_total; set_number++){
for(current_throw = 1; current_throw <= 6; current_throw++){
fscanf(ifp, "%d", &point_val);
if(current_throw <= 3){
points_1 += current_throw;
}
else{
points_2 += current_throw;
}
}
fprintf(ofp,"Set #%d:\n", set_number);
fprintf(ofp,"Student 1: %d points.\n\n", points_1);
fprintf(ofp,"Student 2: %d points.\n\n", points_2);
point_total_1 += points_1;
point_total_2 += points_2;
}
fprintf(ofp,"Final Scores:\n"
"Student 1: %d total points.\n\n", point_total_1);
fprintf(ofp,"Student 2: %d total points.\n\n", point_total_2);
if(point_total_1 > point_total_2){
fprintf(ofp, "Student 1 will move onto the next round!");
}
else if(point_total_2 > point_total_1){
fprintf(ofp, "Student 2 will move onto the next round!");
}
fclose(ofp);
fclose(ifp);
return 0;
}

Answer 1

If I am following along correctly and you need to read the number of sets from the first line, then each set of six values from the lines that follow (one number per-line), producing the output you show of "Set X" followed by the two groups of three values, then your logic shown isn't going to get you there.
This sort of number of sets, groups within each set and number of groups is one that can be handled fairly simply with nested loops. To read the number of sets, you simply read the first value and then you will loop that number of times. That sets the limits for your outer loop for you. For example to read and setup your outer loop you could do:
#include <stdio.h>
#define SETSZ 6 /* if you need a constant, #define one (or more) */
#define GRPSZ 3
#define NGRPS 2
int main (int argc, char **argv) {
int nsets = 0; /* array holding set */
/* use filename provided as 1st argument (stdin by default) */
FILE *fp = argc > 1 ? fopen (argv[1], "r") : stdin;
if (!fp) { /* validate file open for reading */
perror ("file open failed");
return 1;
}
if (fscanf (fp, "%d", &nsets) != 1) { /* read/VALIDATE nsets */
fputs ("error: invalid format - nsets not read.\n", stderr);
return 1;
}
for (int i = 0; i < nsets; i++) { /* loop nsets times */
int set[SETSZ] = {0}; /* array holding set */
/* process remaining sets here */
}
(note: when taking user input, you must VALIDATE every INPUT by checking the return of the input function used. Otherwise, you are just inviting Undefined Behavior in your code on a matching or input failure)
As you loop over each set, you need to:
fill the set with SETSZ values validating each input,
loop NGRPS times processing GRPSZ values from the set,
find the sum of the GRPSZ values, and
output the data in the format shown
In doing so, you can replace the /* process remaining sets here */ placeholder with:
for (int j = 0; j < SETSZ; j++) { /* loop SETSZ times filling set */
if (fscanf (fp, "%d", &set[j]) != 1) { /* read/VALIDATE set value */
fputs ("error: invalid format in set.\n", stderr);
return 1;
}
}
printf ("\nSet %d\n\n", i + 1); /* output set number */
for (int j = 0; j < NGRPS; j++) { /* loop NGRPS times */
int sum = 0; /* declare sum for group of 3 */
putchar ('['); /* output '[' prefix */
for (int k = 0; k < GRPSZ; k++) { /* loop GRPSZ times */
sum += set[j * GRPSZ + k]; /* sum group values */
printf (k ? ", %d" : "%d", set[j * GRPSZ + k]); /* output values */
}
printf ("] = %d\n", sum); /* output result */
}
Other than closing your file, that is the extent of your program. Note, I am simply outputting values to stdout. If you want to write the values to a file, you can simply redirect the output to an output file, e.g. ./program infile > outfile, or you can open another file stream for output and write the values to the file from within the program -- entirely up to you.
Note the program read from the filename provided as the first argument (or reads from stdin by default if no argument is given). The complete example would be:
#include <stdio.h>
#define SETSZ 6 /* if you need a constant, #define one (or more) */
#define GRPSZ 3
#define NGRPS 2
int main (int argc, char **argv) {
int nsets = 0; /* array holding set */
/* use filename provided as 1st argument (stdin by default) */
FILE *fp = argc > 1 ? fopen (argv[1], "r") : stdin;
if (!fp) { /* validate file open for reading */
perror ("file open failed");
return 1;
}
if (fscanf (fp, "%d", &nsets) != 1) { /* read/VALIDATE nsets */
fputs ("error: invalid format - nsets not read.\n", stderr);
return 1;
}
for (int i = 0; i < nsets; i++) { /* loop nsets times */
int set[SETSZ] = {0}; /* array holding set */
for (int j = 0; j < SETSZ; j++) { /* loop SETSZ times filling set */
if (fscanf (fp, "%d", &set[j]) != 1) { /* read/VALIDATE set value */
fputs ("error: invalid format in set.\n", stderr);
return 1;
}
}
printf ("\nSet %d\n\n", i + 1); /* output set number */
for (int j = 0; j < NGRPS; j++) { /* loop NGRPS times */
int sum = 0; /* declare sum for group of 3 */
putchar ('['); /* output '[' prefix */
for (int k = 0; k < GRPSZ; k++) { /* loop GRPSZ times */
sum += set[j * GRPSZ + k]; /* sum group values */
printf (k ? ", %d" : "%d", set[j * GRPSZ + k]); /* output values */
}
printf ("] = %d\n", sum); /* output result */
}
}
if (fp != stdin) /* close file if not stdin */
fclose (fp);
}
Input File
With input from the numbers under your "EDIT:", you would have:
$ cat dat/setsofsix.txt
3
3
3
19
16
8
9
15
1
14
12
13
1
7
8
9
6
6
5
Example Use/Output
The program takes the filename to read as the first argument to the program:
$ ./bin/readsetsofsix dat/setsofsix.txt
Set 1
[3, 3, 19] = 25
[16, 8, 9] = 33
Set 2
[15, 1, 14] = 30
[12, 13, 1] = 26
Set 3
[7, 8, 9] = 24
[6, 6, 5] = 17
Let me know if I understood your problem and whether you have further questions. I'm more than happy to help further.