Issue while creating a simple calculator in C

I am creating a very basic calculator in C but the output is not coming as desired.

#include<stdio.h>
int main(int argc, char const *argv[])
{
    /* code */
    char ch;
    int a,b,p=0;
    scanf("%d",&a);
    while(1)
    {
        ch=getchar();
        if(ch==';')
        {
            p=2;
            break;
        }
        scanf("%d",&b);
        if(ch=='+')
        {
            a+=b;
        }
        if(ch=='-')
        {
            a-=b;
        }
        if(ch=='*')
        {
            a*=b;
        }
        if(ch=='/' && b!=0)
        {
            a/=b;
        }
        if(ch=='/' && b==0)
        {
            printf("INVALID INPUT\n");
            p=2;
            break;
        }
    }

    if(p!=0)
        printf("%d",a);
    return 0;
}

The Output is always coming as the initial value which has been assigned to "a".

Output which is coming-

4
+
5
;
4

Expected output –

4
+
5
;
9

Can you please help me with this issue of why the expression is not getting evaluated correctly?

>Solution :

The line

scanf("%d",&a);

will consume the first number from the input stream, but it will leave the newline character on the input stream.

Therefore, when you later call

ch=getchar();

it will read that newline character. It will not read the + character.

If you want to read the + character, then you can change that line to the following:

scanf( " %c", &ch );

This line will first discard all whitespace characters and will match the first non-whitespace character on the input stream.

Afterwards, your program will have the desired output:

4
+
5 
;
9