Say if I want to ask the user to enter one input or two inputs or three. For example:

int num_1, num_2, num_3;
printf("Enter input" );

Now I'm struggling to find how to scan either one, two or three. If I do this:

scanf("%d %d %d", &num_1, &num_2, &num_3);

it won't work if the user inputs only one or two inputs. So how do I do it?

CodePudding user response：

You should use a cycle and an array for the inputs, for example:

/* array where the inputs will be stored. It has the maximum 
   number of elements (3), assuming you want to use static arrays */
int inputs[3];

int n_inputs, i;
/* ask the user how many values he wants to put */
printf("Number of inputs: \n");
if(scanf("%d", &n_inputs) != 1) {
    fprintf(stderr, "scanf fail!\n");
    exit(EXIT_FAILURE);
}

/* ask for the inputs values */
printf("inputs [%d]: \n", n_inputs);
for(i = 0; i < n_inputs; i  ) {
    if(scanf("%d", &inputs[i]) != 1) {
        fprintf(stderr, "scanf fail!\n");
        exit(EXIT_FAILURE);
    }
}

*edited to add scanf basic error handling.

CodePudding user response：

You can use loop for multiple input. First take the number of input, then loop through that.

For example:

int n, i;
printf("Please enter the input threshold: ");
scanf("%d", &n);

int arr[n];
for (i = 0; i < n; i  ) {
    printf("Enter number #%d: ", i 1);
    scanf("%d", &arr[i]);
}

CodePudding user response：

The following program will read exactly one line of input and read up to MAX_INPUTS (defined as 3) numbers from that line.

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

#define MAX_INPUTS 3
#define MAX_LINESIZE 80

int main( void )
{
    long inputs[MAX_INPUTS];
    int num_inputs;
    char line[MAX_LINESIZE], *p;

    //prompt user for input
    printf( "Please enter up to %d numbers: ", MAX_INPUTS );

    //attempt to read one line of input
    if ( fgets( line, sizeof line, stdin ) == NULL )
    {
        fprintf( stderr, "error reading line\n" );
        exit( EXIT_FAILURE );
    }

    //verify that entire line was read in
    if ( strchr( line, '\n' ) == NULL )
    {
        fprintf( stderr, "line too long\n" );
        exit( EXIT_FAILURE );
    }

    for (
        num_inputs = 0, p = line;
        num_inputs < MAX_INPUTS;
        num_inputs  
    )
    {
        char *q;

        errno = 0;

        //attempt to convert one number
        inputs[num_inputs] = strtol( p, &q, 10 );
        if ( p == q )
            break;

        //make p point to end of inputted number
        p = q;

        //make sure that entered number is representalbe as "long int"
        if ( errno == ERANGE )
        {
            fprintf( stderr, "number is out of range\n" );
            exit( EXIT_FAILURE );
        }
    }

    //output the inputted data
    printf( "You entered %d inputs. The values are:\n" );
    for ( int i = 0; i < num_inputs; i   )
    {
        printf( "%ld\n", inputs[i] );
    }
}

This is what happens when I run this program:

Please enter up to 3 numbers: 80 30
You entered 2 inputs. The values are:
80
30

CodePudding user response：

Use a simple for loop and an array:

int arr[3];

for (int i = 0; i < 3; i  )
     scanf("%d", &arr[i]);