how to scanf unknown amount of integer numbers into array in C? - c

Question

I know that I can scanf certain amount of numbers with scanf for example for 3 numbers
scanf("%d %d %d",array[0],array[1],array[2]);
but how can I scan it if I didn't know how many numbers (integer, not float) I would input into an array before enter (NOT EOF)? for example
input : 12 43 23(enter) --> array[0]=12, array[1]=43, array[2]=23
input : 10 20 30 40 50(enter) --> array[0]=10, array[1]=20, array[2]=30, array[3]=40, array[4]= 50
etc..
It's about how to input the numbers into an integer array.
And if it's possible, I want to save it into an 2 dimensions array, for example
input : 12 43 23(enter) --> array[0][0]=12, array[0][1]=43, array[0][2]=23
input : 10 20 30 40 50(enter) --> array[1][0]=10, array[1][1]=20, array[1][2]=30, array[1][3]=40, array[1][4]= 50

Answer 1

Here is come code showing how to scan the integers into a 2D array:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define INITSIZE 5
#define BUFFSIZE 1000
void print_and_free(int **array, int rowsize, int colsize);
void check_ptr(void *ptr, const char *msg);
int
main(void) {
int **array;
size_t rowsize = INITSIZE, colsize = INITSIZE;
int row = 0, col, numdigits;
char buffer[BUFFSIZE];
char *number;
array = malloc(rowsize * sizeof(*array));
check_ptr(array, "Allocation");
printf("Enter digits(Enter blank line to end):\n");
while (fgets(buffer, BUFFSIZE, stdin) != NULL && strlen(buffer) != 1) {
col = 0;
numdigits = 0;
if (rowsize == row) {
rowsize *= 2;
array = realloc(array, rowsize * sizeof(*array));
check_ptr(array, "Reallocation");
}
array[row] = malloc(colsize *sizeof(int));
check_ptr(array[row], "Allocation");
number = strtok(buffer, " ");
while (number != NULL) {
numdigits++;
if (colsize == numdigits) {
colsize *= 2;
array[row] = realloc(array[row], colsize * sizeof(int));
check_ptr(array[row], "Reallocation");
}
array[row][col] = atoi(number);
col++;
number = strtok(NULL, " ");
}
row++;
}
print_and_free(array, row, col);
return 0;
}
void
print_and_free(int **array, int rowsize, int colsize) {
int row, col;
printf("Your numbers:\n");
for (row = 0; row < rowsize; row++) {
for (col = 0; col < colsize; col++) {
printf("array[%d][%d] = %d", row, col, array[row][col]);
if (col != colsize - 1) {
printf(", ");
}
}
free(array[row]);
array[row] = NULL;
printf("\n");
}
free(array);
}
void
check_ptr(void *ptr, const char *msg) {
if (!ptr) {
printf("Unexpected null pointer: %s\n", msg);
exit(EXIT_FAILURE);
}
}

Answer 2

Here's how you can store things in a (dynamically allocated) array. This does assume that the line length is limited to 1000 chars though. (Code adapted from How do I use scanf() to take an arbitrary amount of integers?)
#include <stdio.h>
#include <stdlib.h>
int main() {
int val_size = 2;
int* vals = (int*)malloc(val_size * sizeof(int)); // initial array size
char buffer[1000]; // for reading in the line
int pos, bytes_read, num;
int num_read = 0;
if (fgets(buffer, sizeof(buffer), stdin) != 0) {
for (pos = 0; sscanf(buffer+pos, "%d%n", &num, &bytes_read) != EOF; pos += bytes_read) {
// resize the array if needed
if (num_read >= val_size) {
val_size *= 2;
vals = (int*)realloc(vals, val_size * sizeof(int));
}
// store the value in the array
vals[num_read] = num;
num_read++;
}
}
// print the values to prove it works
for (int i = 0; i < num_read; i++) {
printf("%d ", vals[i]);
}
printf("\n");
free(vals); // important after you're done with it
}
You can wrap a while around the if to get multiple lines.

Answer 3

You may use a while loop and check for the return value of scanf. For example:
int num = 0;
int idx = 0;
int arr[100] = { 0 };
while( scanf( "%d", &num ) == 1 )
{
arr[idx++] = num;
if( idx == 99 ) // protect from array overflow
{
break;
}
}
for( int i = 0; i < idx; i++ )
{
printf( "%d\n", arr[i] );
}