CODEWITHSUNDEEP
cscanfgetchar
ahmetlutfu
ahmetlutfu

Reputation: 325

Using Scanf after getchar?

I am taking C programming course. I did not understand these codes.

#include <stdio.h>
int main()
{
    int c;
    int ival;
    printf("type : ");
    c = getchar();
    scanf("%d", &ival);
    printf("c     = %d\n", c);  //65
    printf("ival  = %d\n", ival);  //127
    return 0;
}

For example whenever I type Abc, I am getting c = 65; ival = 1. why ival is 1?

Upvotes: 0

Views: 569

Answers (3)

Shahbaz
Shahbaz

Reputation: 47513

ival is never initialized, so it can have any value. The reason is that, c is receiving 'A' (through getchar()) and then scanf fails to read a number (since the next character in the input, 'b', is not a decimal number), so it never touches ival.

You can check the return value of scanf to see if it fails or succeeds:

if (scanf("%d", &ival) != 1)
    printf("you need to enter a number\n");
else
    printf("entered: %d\n", ival);

Note that scanf returns the number of items it successfully read and assigned. For example scanf("%d %f %c", ...) would return 3 if all three items were correctly read.1

1Note that assigned means that ignored input (such as those with the assignment-suppresion modifier (*)) doesn't count towards the return value of scanf (C11, 7.21.6.2.10,16). Furthermore, %n doesn't affect the return value of scanf (C11, 7.21.6.2.12).

Upvotes: 5

Filipe Gon&#231;alves
Filipe Gon&#231;alves

Reputation: 21213

With Abc, getchar() will read A, thus, c will hold the character code for A, which happens to be 65 on your machine (this is the ascii code for A).

For ival, you can get anything: since %d on scanf() expects to read an integer, and you didn't provide one, scanf() returned prematurely, leaving bc in the input buffer, so the value you read from ival when you call printf() is undefined: it can print anything.

Upvotes: 2

haccks
haccks

Reputation: 106012

The reason is that your program invokes undefined behavior.A is read by getchar while bc is left unread by scanf because %d expects to read an integer and hence on encountering the character it stop reading immediately and leave ival uninitialized.

Upvotes: 0

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