getLine is a function that gets a line, I'm trying to combine lines together outside the getLine function. When ever I try doing this in a loop it messes up the output. I bet it has to do with the pointers, but I have spend many hours trying to figure it out.
int num;
int matrix[370];
i=1;
j=0;
while(*(point=getLine(infile)) != -2){
n[j]=*point;
if(n[0] != n[j]){
printf("matrix dim error 1");
break;
}
while (i<=n[j]){
matrix[i+(3*j)] = *(point+(i+(3*j)));
i++;
printf("%d", matrix[i+(3*j)]);
}
printf("%d %d %d\n", matrix[1],matrix[2],matrix[3]);
j++;
}
fclose( infile );
}
int *getLine(FILE *infile){
int l=0;
int line[7];
int i=1;
int *point;
while ((l=getNum(infile)) != -1){
if(l==EOF){
line[0]=EOF;
point = &line[0];
return(point);
}
line[i]=l;
i++;
}
if(i==1){
line[0]=-2;
point = &line[0];
return(point);
}
line[0]=(i-1); //stores the length of the line in first space
printf("%d %d %d\n",line[1],line[2],line[3]);
point = &line[0];
printf("%d\n",*point);
return(point);
}
int getNum(FILE *infile) {
int c=0;
int value=0;
while ((c=fgetc(infile)) != '\n') {
if(c==EOF){
return(EOF);
}
if((c==32)||(c==13)){
if(value != 0){ //Making sure a number has been gotten
//printf("%d\n\n", value);
return(value);
}
//otherwise keep getting characters
}
else if ((c<=47)||(c>=58)){
printf("incorrect number input %d\n", c);
exit(1);
}
else {
value = (10*value) + (c - '0');
}
}
return(-1);//flags that the end of line has been hit
}
There is one problem:
int *getLine(FILE *infile){
int line[7];
int *point;
point = &line[0];
return(point);
}
You return a pointer to a local variable. It becomes invalid when you return from the function. You could allocate it instead on the heap, or let the caller provide it as an argument.
Instead of
while (i<=n[j]){
didn't you mean
while (i<=n[j][0]){
More Edit: That's actually ok, i overlook the * in the assignment.
Edit: Some more things:
there is no check that the range of int is not exceeded in getNum
there is no check in getLine that more than 7 values are read (which would blow int line[7]
the matrix calculation in my opinion assumes that there are 3 values read, getLine can deliver up to 7
matrix[i+(3*j)] = *(point+(i+(3*j))); ?? point is only 7 int big!!! so for the second value it will read beyond defined data. Shouldn't it read matrix[i+(3*j)] = point[i];
hth
Mario
BTW: I strongly recommend:
resort to std-lib functions
better naming (i and j in the same source are strongly discouraged)
Related
So I need output size of array in this file text and to do this I must break the loop in the last position by using NULL to break but the problem here that when arr[i] come to value 0, it equal to NULL and break at that position so my size of array is not complete. How to resolve it? Thanks for support!
The file .txt input:
3
4
0
5
6
The code:
#include <stdio.h>
int main() {
char a[20];
char e[40];
int arr[30];
int num, key, k = 0, len = 0;
printf("Enter a filename: ");
scanf("%s", &a);
scanf("%c", &e);
FILE* rfile;
rfile = fopen(a, "r");
if (rfile == NULL) {
printf("Not found the file !!!");
}
else {
printf("Successfully accessed the file: %s\n", a);
int i;
for (i = 0; i < 30; i++) {
fscanf(rfile, "%d", &arr[i]);
fscanf(rfile, "%c", &e);
if (arr[i] == NULL) { // PROBLEM HERE
break;
}
len++;
}
}
printf("The size of array: %d", len);
return 0;
}
You can find some more details regarding what NULL is here, but you should save NULL for pointer comparisons, not comparing against ints as you are doing. In fact, your usage generates a warning:
warning: comparison between pointer and integer
Despite that, 0 == NULL will evaluate to true. Since 0 is in your list of values, you prematurely break revealing your problem. Instead, you simply need to read the entire file, either until you run out of room in your array (already covered by your for loop) or reach the end of the file (designated by EOF). To determine that, you need to check the return value of fscanf. Below is an example of a possible implementation:
#include <stdio.h>
#include <stdlib.h>
int main() {
int arr[30];
int len = 0;
FILE* rfile;
rfile = fopen("file.txt", "r");
if (rfile == NULL) {
printf("Not found the file !!!");
exit(-1);
}
else {
int i;
for (i = 0; i < 30; i++) {
// fscanf returns the number of correctly matched items, or
// EOF when the end of the file is reached (or EOF on error)
int ret = fscanf(rfile, "%d", &arr[i]);
// did we get a correct match?
if (ret == 1)
{
// we matched one number as expected, increment len
len++;
}
// did we reach the end of file?
else if (ret == EOF)
{
// EOF can also indicate an error, check errno here to determine if
// an error occurred instead of end of file, if you want
break;
}
}
}
// prints 5 with your input file example
printf("The size of array: %d\n", len);
return 0;
}
I have no idea what you were trying to accomplish with e, so I removed that as well as other unused variables, and hardcoded user input.
arr is the array of ints arr[i] has type int. NULL is a pointer.
If 0 indicated the end of the data (sentinel value) then:
if (arr[i] == 0) break;
or in a short form
if (!arr[i]) break;
There is an array of n students( stu[n]).If gender is boy then my code adds
for boy b, 2nd,4th,6th,........even position elements of array and
for girl g, 1st,3rd,5th....odd position elements of array.
1> Gender of boys denoted by b.
2> Gender of girls denoted by g.
Input info>>
The 1st line contains n, denoting the number of students in the class, hence the number of elements in the array.
Each of the subsequent lines contains the marks of n students .
The last line contains gender b/g;
Output info>>
The output should contain the sum of all the alternate elements of marks as explained above.
#include <stdio.h>
int main() {
int n,i;
scanf("%d",&n);//n denotes number of students.
int stu[n],sum=0;
for(i=1;i<=n;++i)
scanf("%d",&stu[i]);//for accepting input in array.
char gen;
scanf("%s",&gen);//for accepting input gender b/g.
for(i=1;i<=n;i++){
if(gen=='g' && i%2!=0){ //girl g adds alternate odd position elements.
sum=sum+stu[i];
printf("%d",sum);
}
else if(gen=='b' && i%2==0){ //boy b adds alternate even position elements.
sum=sum+stu[i];
printf("%d",sum);
}
}
//code
return 0;
}
Sample Input
3
3
2
5
b
Sample Output
8
explanation>>
marks=[3,2,5] and gender = b so it will add 3+5(even position 0,2 alternate elements). If gender in place of b is g then it will produce output = 2.
My code is shows output of 0 in all test cases.
You have the major problem in
int n,i;
int stu[n],sum=0;
here, n being a uninitialized local scoped variable with automatic storage, the initial value is indeterminate.
Now, since the address of the variable was never taken and it has a type that can have trap representation, attempt to use the value (int stu[n]) will invoke undefined behavior.
You need to scan in the value into n first, then use that to define the VLA stu. Something like
int n,i;
scanf("%d",&n);//n denotes number of students.
// **Note: please check for errors in input with scanf return value.**
int stu[n],sum=0; // here, n has the scanned value.
That said,
char gen;
scanf("%s",&gen);
is also horribly wrong, you want to scan in a char, not a string, and with the address of a plain char variable, %s conversion specification would be UB, again. You should use %c and discard any whitespaces which is present in buffer altogether.
You're making things more complicated than they need to be. Here is how you can possibly do:
#include <stdio.h>
int main(void)
{
int mark;
int b = 0;
int g = 0;
char students_marks[5];
for (int i=0; i<5; i++) {
scanf("%d", &mark);
students_marks[i] = mark;
}
for (int i=0; i<5; i++) {
if (i%2 == 0) b += students_marks[i];
if (i%2 == 1) g += students_marks[i];
}
printf("Boys: %d\nGirls: %d\n", b, g);
return 0;
}
You should probably not use an array, and just ignore the first data point. It is (probably) easier to use a linked list. Or maybe just use two lists, alternating the inputs between them. And I would definitely not use scanf. If you are new to C, do NOT waste your time learning the foibles of the scanf format string language. The only time scanf is ever useful is in introductory courses where instructors incorrectly believe that you will be able to get input more quickly than if you spend time learning other methods. But in fact you will end up burning more time learning when to use spaces in the format string that you saved by not learning fread. After your introduction to C, you will (almost) never use scanf. Also, it seems like a horrible design to put the discriminant at the end of the input. The values to be summed (the gender) should be given as a command line argument. That said, you could just do:
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
FILE *
xfopen(const char *path, const char *mode)
{
FILE *rv;
if( (rv = fopen(path, mode)) == NULL ) {
perror(path);
exit(EXIT_FAILURE);
}
return rv;
}
int
main(int argc, char **argv)
{
int i;
int size; /* Should probably be size_t. Skipping that for now. */
FILE *in = argc > 1 ? xfopen(argv[1], "r") : stdin;
int sum = 0;
if( fscanf(in, "%d", &size) != 1 || size <= 0 ) {
fprintf( stderr, "invalid input\n" );
exit(EXIT_FAILURE);
}
int grades[size];
for( i = 0; i < size; i++ ) {
if(fscanf(in, "%d", grades + i) != 1) {
fprintf( stderr, "invalid input on line %d\n", i );
exit(EXIT_FAILURE);
}
}
char gender;
if(fscanf(in, " %c", &gender) != 1) {
fprintf( stderr, "invalid input on line %d\n", i );
exit(EXIT_FAILURE);
}
if(strchr("bBgG", gender) == NULL) {
fprintf( stderr, "invalid gender: %c\n", gender);
exit(EXIT_FAILURE);
}
for( i = tolower(gender) == 'b'; i < size; i += 2 ) {
sum += grades[i];
}
printf("sum: %d\n", sum);
}
Hmm… i changed your code a Little bit and hope this runs as described.
int main() {
int n, index, sum=0;
int* stu;
scanf("%d", &n); // input number of studens
if(n>0)
stu = malloc(n*sizeof(int)); // allocate memory
else
return 0;
for(index=0;index<n;index++)
scanf("%d", &stu[index]);
char gen;
scanf("%c", &gen);
for(index=0; index<n; index++){
if(gen=='g' && index%2!=0) {
sum += stu[index];
printf("%d", sum);
} else if(gen=='b' && index%2==0) {
sum += stu[index];
printf("%d", sum);
}
}
return 0;
}
sorry if the title is non-specific but I wasn't too sure of how I was supposed to title this post. I'm creating a function which encrypts a given string. Here it is:
int ind(char c, char * t){
int i = 0;
while (i != strlen(t)){
if (t[i] == c) return i;
}
return -1;
}
void translate2 (char * c, char * ret){
char used[1000], d;
int i = 18, size = 0;
for (i=0; i < strlen(c);i++){
printf("\nChar: %c",c[i]);
printf("arguments going in are char %c and str %s", c[i], used);
if (ind(c[i], used) == -1){
used[size] = c[i];
ret[size] = c[i];
size++;
}
else{
if (ind(c[i], used) == 0){
d = used[size];
}
else {d = used[ind(c[i], used)-1];}
/*printf("Thus, our d shall be %c\n\n", d);*/
ret[size] = d;
size++;
}
printf("\nSeq: %s", used);
printf("\nOutput: %s\n", ret);
}
}
Sorry if the code is messy, I'm pretty new to this. I suppose what the code actually does isn't too important. My issue here is that, the code works as intended for the first run through the loop. Once it finishes that, the program stops. I can't figure out why this happens, and I'm not handy enough with debuggers to use them. Can anyone point me towards the right direction? Any help is appreciated. Thanks!
while (i != strlen(t)){
if (t[i] == c) return i;
}
‘i’ is not incrementing in the loop. You are indefinitely checking the first element
I am trying to load elements into an array using a function but I don't know what I'm doing wrong. I want to load elements from a data file until -1 is entered. Here is what I have and I don't know what to do from here.
#include <stdio.h>
/*Function to scan in grades*/
int LoadArray (int grade[ ])
{
int i = 0;
while(scanf("%i", grade[i]) != -1) {
i++;
}
return i;
}
/*Main program*/
int main (void)
{
int grade[200], count=0;
/*Call function*/
count = LoadArray(grade);
printf("%i", count);
return 0;
}
Two problems.
1) You're missing an ampersand:
scanf("%i", &grade[i]);
you need to pass the address of the variable scanf should put the result in. You were passing the contents of grade[i] instead, and reading uninitialized memory is undefined behavior.
2) scanf doesn't return the value it read from stdin; you should compare the variable you read to -1. Also, it's bad practice to pass an array to a function but not its size, as then the function has no way of knowing how big the array is.
To sum up, the code with fixes looks like this:
/*Function to scan in grades*/
int LoadArray(int grade[], size_t gradeMaxCount)
{
int i = 0;
while (1)
{
int tmp;
if (i >= gradeMaxCount || scanf("%i", &tmp) != 1 || tmp == -1)
break;
grade[i++] = tmp;
}
return i;
}
Call the function like this:
count = LoadArray(grade, sizeof(grade) / sizeof(grade[0]));
Note that funny things will happen if i somehow becomes negative. You could make it size_t instead (this would also require you to change the function return type and print it using %zu), depending on how much of a purist you are.
int LoadArray (int grade[ ])
{
int i = 0;
for(int j=0;j<200;j++){
if((scanf("%d", grade+j) == -1) || (grade[j]==-1))
break;
i++;
}
return i;
}
My program needs to read input from a file. The file has a format "int int int" and then some asterisks to indicate that you need to stop reading there. I want to store them in an array of struct and I did. But it seems like my program can't read the very first integer of the input file. I checked it with printf and I can't do anything about it. Help please. Here's the code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct points{
int i;
int x;
int y;
};
int main(){
int lines = 0;
char c, e;
int i, j, x ,y, a, b, temp ;
FILE *fp;
fp = fopen("input.txt", "r");
if (fp != NULL){
while ((e = fgetc(fp)) != '*'){
if (c == '\n'){
lines++;
}
fscanf(fp, "%d%d%d", &i, &x, &y);
struct points pt[lines];
for (j = 0; j <= lines; j++){
pt[j].i = i;
pt[j].x = x;
pt[j].y = y;
printf("%d ", pt[j].i);
}
for (a = 0; a<=lines; a++){
for (b = a + 1; b <= lines; b++){
if (pt[a].x > pt[b].x){
temp = pt[a].x;
pt[a].x = pt[b].x;
pt[b].x = temp;
}
}
}
}
}
else{
printf("Cannot open File!\n");
}
printf("lines = %d\n", lines);
return 0;
}
Your code:
while ((e = fgetc(fp)) != '*') {
if (c == '\n'){
lines++;
}
fscanf(fp, "%d%d%d", &i, &x, &y);
will read the first character and throw it away if it is NOT an asterisk, and will then attempt to read 3 integers AFTER that first character it threw away. If that first character was a digit, then it will look like you 'lost' (part of) the first number.
You also have the problem that you seem to be trying to read the values into a block-local array pt that exists for a single iteration of the while loop (so its recreated with no (garbage) contents each iteration), and then you want to use it after the loop where it is out of scope (so this code won't compile).
What you want is probably something more like:
#define MAX_POINTS 100
struct points pt[MAX_POINTS];
int i = 0;
while (i < MAX_POINTS && 3 == fscanf(fp, "%d%d%d", &pt[i].i, &pt[i].x, &pt[i].y)) {
printf("%d ", pt[i].i);
i++;
}
for (int a = 0; a <= i; a++) {
for (int b = a+1; b <= i; b++) {
:
Note that this reads integers up until it finds something that doesn't look like an integer (such as an asterisk, but could be anything else, including an end-of-file), rather than reading until it finds an asterisk. If you want to read until you see an asterisk, you need to decide what to do with anything that is neither an asterisk or an integer.
Edit
for your alternate question of how to read numbers up to *** and then read more numbers after them (and possibly more stars), you could use something like:
int val;
char buffer[20];
do {
/* start of a group */
while (1 == fscanf(fp, "%d", &val)) {
/* read an integer within a group */
}
/* fp is at EOF or something not an integer. */
/* so read it and loop if its '***' */
} while (1 == fscanf(" %19[*]", &buf) && !strcmp(buf, "***"));
Have you tried using the format string "%d %d %d" instead of "%d%d%d" (i.e. with spaces)?
Also, there are several other problems I see:
You use a while loop to find the first '*' in the line, but then you ask fscanf to parse 3 ints starting at that location. It may not be able to find an int by looking at a '*'...
You also declare the variable struct points pt[lines]; in the middle of a block; that is not valid C syntax.
Once you fix these things, the problem may be fixed.