C Calculator With getchar/putchar - c

Question

First time ever C programming class. I have to create a C calculator using putchar/getchar. The code below if what I have to far and loops to ask the user for input. The issue I am having is how to account for space/multiple spaces before input, space/multiple spaces between the digits and operand, no spaces between operand and digits, and spaces after input by the user is complete.
Right now the code will work with one space between the digits and operand.
Meaning, 10 + 5 works. However, for example, 10+5 does not and ____5 + 10 (where __ = space), or 10+5______, or 10_________+ 10 do not work.
Any advice or help on how to account for multiple spaces in between the digits and operand and before after any user input is so very greatly appreciated.
Thank you so very much for any and all help with the current code. Really do appreciate your help and time!!
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <math.h>
int add(int input1, char operand, int input2);
int subtract(int input1, char operand, int input2);
int mod(int input1, char operand, int input2);
int multiply(int input1, char operand, int input2);
int divide(int input1, char operand, int input2);
char cont(void);
int main()
{
int answer = 0;
int ch = 0;
int input1 = 0;
char operand = 0;
int input2 = 0;
int function = 0;
char flag;
do {
input1 = 0, input2 = 0, operand = 0;
printf("\nPlease enter a calculation to be made.\n");
while (((ch = getchar()) != ' ') && (ch != EOF) && (ch != '\n')){
if (ch == '-') {
printf("\nError: no negatives allowed.\n");
}
else if (!isdigit(ch)){
printf("\nError: number not inputted (first number).\n");
}
else {
input1 = (input1 * 10) + (ch - '0');
}
}
while (((ch = getchar()) != ' ') && (ch != EOF) && (ch != '\n')){
switch (ch){
case '+':
operand = '+';
break;
case '-':
operand = '-';
break;
case '%':
operand = '%';
break;
case '*':
operand = '*';
break;
case '/':
operand = '/';
break;
default:
printf("Error: input is not one of the allowed operands.");
break;
}
}
while (((ch = getchar()) != ' ') && (ch != '\n')){
if (ch == '-') {
printf("\nError: no negatives allowed.\n");
}
else if (!isdigit(ch)){
printf("\nError: number not inputted (second number).\n");
}
else {
input2 = (input2 * 10) + (ch - '0');
}
}
printf("%d", input1);
putchar(' ');
printf("%c", operand);
putchar(' ');
printf("%d", input2);
putchar(' ');
putchar('=');
putchar(' ');
if (operand == '+'){
answer = add(input1, operand, input2);
printf("%d", answer);
}
else if (operand == '-'){
answer = subtract(input1, operand, input2);
printf("%d", answer);
}
else if (operand == '%'){
answer = mod(input1, operand, input2);
printf("%d", answer);
}
else if (operand == '*'){
answer = multiply(input1, operand, input2);
printf("%d", answer);
}
else if (operand == '/'){
answer = divide(input1, operand, input2);
printf("%d", answer);
}
flag = cont();
}
while (flag == 'y' || flag == 'Y');
return 0;
}
int add(int input1, char operand, int input2){
return input1 + input2;
}
int subtract(int input1, char operand, int input2){
return input1 - input2;
}
int mod(int input1, char operand, int input2){
return input1 % input2;
}
int multiply(int input1, char operand, int input2){
return input1 * input2;
}
int divide(int input1, char operand, int input2){
return input1 / input2;
}
char cont()
{
char flag;
printf("\nDo you want to process another calculation (y/n)? ");
scanf("%c%*c", &flag);
return flag;
}

Answer 1

Ok! the solution to this problem involves understanding how getchar() works. It also includes a concept of how input from standard input [stdin] works.
So, whenever input to variables is taken using scanf()/getchar() etc. either operations are required in order to alert the compiler that the input for the variable is confirmed. One is new line \n(Pressing Enter) and the other is white-space. They will alert that the input is finalized.
This is explained by input 10 + 5 [Press Enter]. The first space ensures ch has values 10 and thus input1 has a value 10. Then + come through and after the space the operand gets the value of +. Later, Enter is pressed after writing 5. This will save value 5 in input2. The rest of the operations happen perfectly.
In other cases where we have so many spaces ____5 + 10 / 10+5______ / 10_________+ 10 we must look at how the code will follow on such input.
_____5+10 The first space will miss the first while loop because space is an exit condition. The control then goes to the second while loop, where second space will also be an exit condition for the loop. The same happens to the third while loop and it also exits. Thus, the answer will be input1 operand input2 and all these have default values i.e. 0, 0 (which is blank when scaled down to character) and 0 respectively.
10+5_____ Here the first space appear after 5, thus, the getchar() will feed input1 with values 10+5and other two variables don't even get assigned.
This shows why the variables couldn't get assigned the values we expected. The solution for this problem can be solved by extra processing but performing checks on how spaces appear.