Store string with numbers as an integer array

Question

I'm writing a program in C where there's a user input. This input is a string with integer values separated by a space. The numbers (except the first one) have to be stored in an integer array. The first number indicates how many numbers have to be stored (so the size of the array).

What's the easiest way to do this in C? Here's an example:

input--> "5 76 35 95 14 20"

array--> {76, 35, 95, 14, 20}

I've been searching around but I can't find a solution to my question. At the moment, I've tried to store the values of the input in a char array and, when there's a space, I convert this string to an integer using atoi() and I add it to the integer array. But it prints strange values. This is the code:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    char text[10];
    scanf("%s", text);

    int nums[4];
    int indNs = 0;

    char lastNum[10];
    int indLN = 0;

    for(int i = 0; i < 10; i++)
    {
        if(text[i] == ' ')
        {
            nums[indNs] = atoi(lastNum);
            indNs++;

            sprintf(lastNum, "%s", "");
            indLN = 0;
        } else
        {
            lastNum[indLN] = text[i];
            indLN++;
        }
    }

    nums[indNs] = atoi(lastNum);

    for(int i = 0; i < 4; i++)
    {
        printf("%d\n", nums[i]);
    }
}

Like `int array[5]; int unused; sscanf(input, "%d %d %d %d %d %d", &unused, &array[0], &array[1], &array[2], &array[3], &array[4])`? — KamilCuk, Jun 14 '19 at 17:08
@ARD Look at my link. I answered a similar question earlier. — klutt, Jun 14 '19 at 17:14
@ARD Ups. I picked the wrong link even if that one also helps, but this is better: https://stackoverflow.com/a/56570260/6699433 — klutt, Jun 14 '19 at 17:16

kiran Biradar · Accepted Answer · 2019-06-15T04:08:24.523

You cannot use scanf to read space separated input as scanf will stop reading once it hits white space.

scanf("%s", text); //Wrong, always reads only first number.

You could use fgets followed by sscanf with %n in loop.

char buf[100];

int *array = NULL;
int numElements = 0;
int numBytes = 0;
if (fgets(buf, sizeof buf, stdin)) {

   char *p = buf;
   if (1 == sscanf(buf, "%d%n", &numElements,&numBytes)){
       p +=numBytes;
       array = malloc(sizeof(int)*numElements);
       for (int i = 0;i<numElements;i++){
         sscanf(p,"%d%n", &array[i],&numBytes);
         p +=numBytes;
         printf("%d,", array[i]);
       }
   }
}

%n returns number of bytes read so far thus advance the buf number of bytes read so far.

If you are not dealing with strings and directly reading from stdin you don't need all that mess.

int *array = NULL;
int numElements = 0;


scanf("%d", &numElements);
array = malloc(sizeof(int)*numElements);

for(int i=0;i<numElements;i++)
{
    scanf("%d", &array[i]);
    printf("%d ", array[i]);
}

There is no need to read the whole line into a buffer, just read each integer separately using `scanf("%d", &foo)` — HAL9000, Jun 14 '19 at 20:03

Vlad from Moscow · Answer 2 · 2019-06-14T17:28:03.510

In this case you can use for example the standard C function strtol declared in header <stdlib.h>.

For example

#include <stdio.h>
#include <stdlib.h>

int main( void )
{
    const char *s = "5 76 35 95 14 20";

    char *p = ( char * )s;

    int n = ( int )strtol( p, &p, 10 );

    int *a = malloc( n * sizeof( int ) );

    for ( int i = 0; i < n; i++ )
    {
        a[i] = strtol( p, &p, 10 );
    }

    for ( int i = 0; i < n; i++ )
    {
        printf( "%d ", a[i] );
    }
    putchar( '\n' );

    free( a );
}

The program output is

76 35 95 14 20

To read a string with blanks you should use the standard C function fgets.

Store string with numbers as an integer array

2 Answers2