How to compute multiplication on multi-digit numbers by reading characters one by one

Question

So basically I must make it work with multiplication as well with signs.For example 2*2=4 but 2*-2=-4 and i cant find a proper way to do it.Any advice would be helpful.My code so far is :

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

int main ( void )
{
    int result = 0, val = 1, ch, howmany = 1, number = 0;
    while ( ( ch = getchar() ) != EOF )
    {
        if ( ch == ' ' || ch == '\t' )
            continue;
        else if ( ( ch >= '0' ) && ( ch <= '9' ) )
            number = number * 10 + ( ch - '0' );
        else if ( ch == '+' )
        {
            result += ( number * val );
            val = 1;
            number = 0;
        }
        else if ( ch == '-' )
        {
            result += ( number * val );
            val = -1;
            number = 0;
        }
        else if ( ch == '\n' )
        {
            howmany++;
            result += ( number * val );
            printf( "%d\n", result);
        number = 0;
        result = 0;
        val = 1;
    }
}
 }

can you give us more details as to what your program does? As in, how is it broken? Maybe some sample inputs and outputs — CoffeeTableEspresso, Dec 04 '18 at 20:43
`i can't make it work` is not a good description of the problem. — Osiris, Dec 04 '18 at 20:43
Give us an example of some input and the output you see, and the output you want to see. — Tim Randall, Dec 04 '18 at 20:43
It works like a charm, but you have to press Ctrl-D to send an end of file, and break out of the loop. — HAL9000, Dec 04 '18 at 20:44
@HAL9000 On unix-like systems Ctrl+D is EOF; on Windows/DOS it is Ctrl+Z — Govind Parmar, Dec 04 '18 at 20:46
Try another `else if (ch == 'x') break;` and type an 'x' on the input. — pmg, Dec 04 '18 at 20:46
Maybe it would be easier to use if you break out of the loop as soon as the user enters something that isn't a digit — Tim Randall, Dec 04 '18 at 20:55
Duplicate of https://stackoverflow.com/questions/11968558/how-to-enter-the-value-of-eof-in-the-terminal — Antti Haapala -- Слава Україні, Dec 04 '18 at 21:10
I need it for a 'calculator' that reads it's input digit by digit with getchar().It prints the result every time you hit enter and it terminates when you enter EOF(ctrl D).The given part may print the number when you press eof but i need it to do it when you hit enter. — , Dec 04 '18 at 21:28
@mouratios Check if getchar() returns `'\n'` ( a newline). if it does, print the number. — nos, Dec 04 '18 at 22:04
I updated the post with all the code.I seem to always get 0 as result. — , Dec 04 '18 at 22:08

score 1 · Accepted Answer · answered Dec 04 '18 at 22:23

1

The code is zeroing the result on every loop iteration.

It seems like it should only do this after printing the result variable.

    else if ( ch == '\n' )
    {
        howmany++;
        result += ( number * val );
        printf( "%d\n", result );
    }
    number = 0;
    result = 0;
    val = 1;

Should be:

    else if ( ch == '\n' )
    {
        howmany++;
        result += ( number * val );
        printf ( "%d\n", result );

        number = 0;
        result = 0;
        val = 1;
    }

With this change, it works for me (pressing [enter] after each arithmetic expression):

$ ./calc_code
1+1
2
3+2
5
-1+1
0
7+2
9
7-2
5
7+13
20

answered Dec 04 '18 at 22:23

Kingsley

14,398
5
31
53

First of all thanks for the help.In order to complete it I must make it work with multiplication as well with signs.For example 2*2=4 but 2*-2=-4 and i cant find a proper way to do it.Any advice would be helpful. – Dec 05 '18 at 13:06
@mouratios Maybe you could consider handling brackets, and when you read `(` store the current result, calculate the next expression until a `)` is read. Note also that when you hit 2 operators together, it should always be this `[any operator][-]Value` form (or a syntax error). Googling "parsing numerical expressions" should give you a few ideas too. – Kingsley Dec 05 '18 at 22:05

How to compute multiplication on multi-digit numbers by reading characters one by one

1 Answers1