scanf getchar function is skipped

Question

A very simple question. Why scanf is skipped in the first while loop. I have tried it by using getchar() and the result is same. getchar is skipped.

If you guys dont understand what I'm talking about you can tried compile it and you guys will understand what i'm asking about.

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

typedef struct rec{
    int num;
    char pref[16];
    float point;
    struct rec* next;
}rec;

void dataInput(float*,char*);
rec* insertNode(rec*);

int main(){

    int i=1;
    rec* entr,*pt = NULL;
    entr = (rec*) malloc(sizeof(rec));
    entr->num = i;
    dataInput(&entr->point,entr->pref);
    entr->next = NULL;
    char key;
    i++;

    while(1){

        printf("Continue ? If YES press 'y',or NO press 'n'\n");
        key = getchar();
        if(key == 'n')break;
        else if(key == 'y'){
            if(!pt){
                pt = insertNode(entr);
            }else{
                pt = insertNode(pt);
            }
            dataInput(&pt->point,pt->pref);
            pt->num = i;
            i++;
            continue;
        }else{
            printf("Wrong key! Please Press again! \n");
        }

    }

    pt = entr;
    while(pt){

        printf("num : %d, pref :  %s, point: %.1f\n",
                pt->num,
                pt->pref,
                pt->point);
        pt = pt->next;
    }

    getchar();
    getchar();
    return 0;
}

void dataInput(float* point,char* pref){

    printf("Input Point\t : ");
    scanf("%f",point);

    printf("Input Pref\t : ");
    scanf("%s",pref);
}

rec* insertNode(rec* current){
    rec* newnode = (rec*)malloc(sizeof(rec));
    current->next = newnode;
    newnode->next = NULL;
    return newnode;
}

raina77ow · Accepted Answer · 2012-11-20 12:59:36Z

8

It's because scanf will leave a '\n' (endline) symbol in the input buffer. This symbol will be consumed by getchar at the first iteration of this while(1) loop.

answered Nov 20, 2012 at 12:59

raina77ow

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1 Comment

edisonthk Over a year ago

Yes! it works!! if(key == '\n'){ key = getchar(); } after i added it. Thank you

P.P · Accepted Answer · 2012-11-20 13:02:25Z

6

getchar() leaves a newline character in the input buffer which is read by the subsequent scanf().

You can use solve this by using a leading space in the scanf:

scanf(" %c ...", &c,..);

which tells the scanf to ignore all whitespace characters. Or use another getchar() right after the first getchar() to consume the newline.

answered Nov 20, 2012 at 13:02

P.P

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2 Comments

the_endian Over a year ago

Omg this second option you suggested has been the ONLY WORKING OPTION for me. I tried everything mentioned in the nearly 15 similar questions. Adding a space before the %c didn't work, adding a \n after the %c didn't work, using fflush(stdin) didn't work, gets, getchar, and scanf all had the same problem... Ugh... Do you know why this is?

P.P Over a year ago

Could be due to any subsequent scanf/fgets calls etc. Can't tell without looking at the code. But I'd suggest reading this: c-faq.com/stdio/scanfprobs.html and avoid scanf() altogether.

Shaik Mohammed Zeeshan · Accepted Answer · 2020-07-18 04:50:51Z

1

Just use another getchar() after the scanf() to consume the newline character.

answered Jul 18, 2020 at 4:50

Shaik Mohammed Zeeshan

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