Using a while loop to iterate through user input until specific number

Question

I am trying to print out each integer on a new line, given integers separated by whitespace from a user input. It stops printing after a specific number, lets say 84. For example

The user input is

20 -4 84 8

How could i use a while loop to print these out as

20
-4
84

i know about scanf("%d %d %d %d", a, b, c, d), However the input size would be unknown, such that there could be only 3 numbers or 7 numbers. So far i have:

#include <stdio.h>

int main(void)
{
    int i = 0;
    int x = 0;
    scanf("%d", &x);
    while (x != 84) {
        print("%d\n", x[i]);
        i++;
    }
}

sorry editing the question. it is the 'x' which is the user input. No not looking to store previous numbers, just needing to print them — Jack8246
– Jack8246, Commented Jul 22, 2015 at 5:51

Shreevardhan · Accepted Answer · 2015-07-23 14:01:23Z

4

Push the scanf into the while condition. Something like

while (scanf("%d", &x) != EOF && x != 84)
    print("%d\n", x);

edited Jul 23, 2015 at 14:01

answered Jul 22, 2015 at 5:54

Shreevardhan

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8 Comments

Peter Cordes Over a year ago

+1 for checking the return value of scanf, to avoid inf-loop when user enters something that "%d" won't scan.

Jack8246 Over a year ago

Thank you this is exactly what i needed. Could you explain to me how putting the scanf inside the while condition works compared to what i was doing? I am new to C, thanks

Shreevardhan Over a year ago

@Jack8246 You scanned for input once and compared to 84 again and again, this scans until 84 is found. That's the difference. This also checks if scanf correctly reads what it is asked to, int here.

Jack8246 Over a year ago

@Shreevardhan I see, so by putting the scanf into the while loop, does the while loop automatically iterate through each integer from the user input? This is the main thing I'm not sure about, hence why i had the 'i++' in my previous code

Shreevardhan Over a year ago

@Jack8246 Yes. scanf("%d", &x); scans an integer in x. Putting this inside a loop condition will execute it in every loop iteration until the loop breaks. So, it scans integers until it finds 84. You can read a good book on C programming to get better idea.

|

Sourav Ghosh · Accepted Answer · 2015-07-22 05:59:26Z

2

The basic concept should be of two-steps:

Read the number
Check and decide whether to print /continue.

A psuedo-code would look like

while ((ret =scanf(x)) && ret != EOF ){
     if (x == VAL) break;
     printf(x);
 }

answered Jul 22, 2015 at 5:59

Sourav Ghosh

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Comments

enrico.bacis · Accepted Answer · 2015-07-23 13:52:05Z

0

You have a few errors:

the array num does not exist;
the scanf must be repeated inside the while loop.

The corrected code is thw following:

#include <stdio.h>

int main(void)
{
    int x;
    while( 1 ){
        scanf( "%d", &x );
        print( "%d\n", x );
        if( x==84 ) break;
    }
}

edited Jul 23, 2015 at 13:52

answered Jul 22, 2015 at 5:54

enrico.bacis

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2 Comments

Jack8246 Over a year ago

the array num was supposed to be 'x', sorry about that. Thanks for the answer

user3629249 Over a year ago

this answer is almost right; however, the OP indicated the 84 was to be printed. so the 'if()' statement and the printf() statement need to be swapped. BTW: it is 'printf' not 'print' and the returned value (not the parameter value) also needs to be checked, so something like a user input that is not digits, like a simple newline and/or a...z, etc can be caught, when the returned value is not 1, need a call to getchar() rather than a call to printf() and if returned value is EOF, then need to exit loop

raymelfrancisco · Accepted Answer · 2016-09-04 06:57:43Z

-1

You need to put scanf() inside the while loop in order to update every new input. No need for arrays if you want to print only the inputted values because you can print it after new input. Better do it with do-while loop.

#include <stdio.h>

int main(void)
{
    int i = 0;
    int x = 0;

    do {
        if ( scanf("%d", &x) < 0 )
            break;
        printf("%d\n", x);
    } while (x != 84);
}

edited Sep 4, 2016 at 6:57

answered Jul 22, 2015 at 5:54

raymelfrancisco

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