Input by use in code 2 vs 1 for command

Question

1.00/5 (2 votes)

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CODE 1

#include <stdio.h>
int main()
{

    int a;

    printf("Enter the value of a\n");
    scanf("%d", &a);

    int c;

    printf("Enter the value of c\n");
    scanf("%d", &c);

    char command;

    printf("Enter the  command \n");
    scanf("%c", &command);
 printf("Enter the  command \n");
    scanf("%c", &command);
    if (command == '+')
    {
        printf("%d ", a + c);
    }

    if (command == '-')
    {
        printf("%d ", a - c);
    }
    return 0;
}

// VS code 2

#include <stdio.h>
int main()
{

    int a;

    printf("Enter the value of a\n");
    scanf("%d", &a);

    int c;

    printf("Enter the value of c\n");
    scanf("%d", &c);

    char command;

 printf("Enter the  command \n");
    scanf("%c", &command);
    if (command == '+')
    {
        printf("%d ", a + c);
    }

    if (command == '-')
    {
        printf("%d ", a - c);
    }
    return 0;
}

What I have tried:

I have faced this problem with scanf many times

Posted 24-Jul-22 3:13am

Aayush Jain 2022

Updated 24-Jul-22 6:42am

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Comments

Greg Utas 24-Jul-22 9:24am

What problem have you faced with scanf? You haven't told us.

Richard MacCutchan 24-Jul-22 12:13pm

See my answer below.

3 solutions

Solution 3

As Richard said, we had already discussed the basic problem.

C

int c;

printf("Enter the value of c\n");
scanf("%d", &c);

char command;
    
printf("Enter the  command \n");
scanf("%c", &command);
printf("Enter the  command \n");
scanf("%c", &command);

The first entry is skipped directly because the end-of-line character from the previous entry was still in the buffer. So it would make sense to read until the end of line character was read.

You need something like this:

C

char c
do { scanf("%c", &c);} while (c != '\n');

Posted 24-Jul-22 6:42am

merano99

Updated 24-Jul-22 6:48am

v2

Solution 2

You were given a suggested solution in your original post at Why when subtracting I am not getting value of C[^]. Please do not repost.

Posted 24-Jul-22 6:13am

Richard MacCutchan

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Greg Utas · Accepted Answer · 2022-07-24T03:34:00

I will guess that you have a whitespace problem. See this write-up on scanf[^]. That's my go-to site when I have detailed questions about C++. It's also great for C, which I don't use. Note the example part way down, which looks very much like yours:

C

scanf("%d", &a);
scanf(" %c", &c); // consume all consecutive whitespace after %d, then read a char

Note the space at the beginning of their " %c". This suggests that there was still whitespace in the buffer after you read the second integer, and that your first call to scanf returned it (probably a '\n') before the second one read the character that you entered.

You would have figured this out if you had checked if c was a '+', '-', or something else. scanf also returns an int, which indicates whether it succeeded, and this is also something that you should check. Simply assuming that your code works leads to this kind of bewilderment. When you work on large programs that need to be resilient, as much as 90% of the code involves checking for, and handling, error situations.