Answer to Question #206407 in C for Tom Boyle

Question

Create a grammar for a calculator that operates using the four operations only (ADD, SUB, MUL, DIV) over hexadecimal numbers.

Answer 1

#include<stdio.h>
#include<conio.h>
#include<math.h>


int hexToDecimal (char hexnum[]) {
    int decnum = 0, rem, i = 0, len = 0;
    while (hexnum[i] != '\0') {
        len++;
        i++;
    }
    len--;
    i = 0;
    while (len >= 0) {
        rem = hexnum[len];
        if (rem >= 48 && rem <= 57)
            rem = rem - 48;
        else if (rem >= 65 && rem <= 70)
            rem = rem - 55;
        else if (rem >= 97 && rem <= 102)
            rem = rem - 87;
        else {
            printf("\nYou've entered an invalid Hexadecimal digit");
        }
        decnum = decnum + (rem * pow(16, i));
        len--;
        i++;
    } 
    return decnum;
}
int main() {
    int firstDecNumber, secondDecNumber;
    char first[20], second[20];
    char operator;
    printf("Enter an operator (+, -, *,): ");
    scanf("%c", &operator);
    
    printf("Enter two operands: \n");
    printf("Enter first Hexadecimal Number: ");
    scanf("%s", first);
    printf("Enter second Hexadecimal Number: ");
    scanf("%s", second);
    
    firstDecNumber = hexToDecimal(first);
    secondDecNumber = hexToDecimal(second);
    
    switch (operator) {
    case '+':
        printf("%d + %d = %d", firstDecNumber, secondDecNumber, firstDecNumber + secondDecNumber);
        break;
    case '-':
        printf("%d - %d = %d", firstDecNumber, secondDecNumber, firstDecNumber - secondDecNumber);
        break;
    case '*':
        printf("%d * %d = %d", firstDecNumber, secondDecNumber, firstDecNumber * secondDecNumber);
        break;
        // operator doesn't match any case constant
    default:
        printf("Error! operator is not correct");
    }
    
    getch();
    return 0;
}