为什么在加法和减法工作正常的情况下，计算器在相乘和相除时总是给我0？

我只是想用C语言制作一个计算器。当我使用加法和减法时，程序运行良好，但是，当我尝试除法或乘法时，无论我提供什么输入，程序都将返回错误。

这是我的代码。在这种情况下，我只是简单地使用goto语句而不是循环来进行多个用户输入（例如1 + 2 + 3 + ....）的循环b，然后将先前的值保存回变量，然后询问另一个值并保存在variable中c。

我只是想不出我的错误，任何帮助将不胜感激。

#include <stdio.h>

int main() {
    int a, d;
    double b=0,c=0;
    printf("This is a CLI Based calculator program!\nSelect what do you want to do?!");
    Restart:        //If user still want to continue with current results
    printf("\n1: Addition\t\t2: Subtraction\n3: Multiplication\t4: Divide\n");
    printf("\nChoose option:");
    scanf("%d",&a);
    //Check if user has previously used the program or not
    if(b==0) {
        printf("Enter First Number: ");
        scanf("%d",&b);
    } else {
        printf("\nYour Previous result is :%d", b);
        printf("\nEnter Another Number: ");
        scanf("%d",&c);
        goto Continue;
    }
    printf("Enter Second Number: ");
    scanf("%d",&c);
    Continue:       //Resume process from here if user wants to continue
    switch (a) {
        case 1:
            printf("This is Addition: %d\n", b+c);
            b = b+c;
            break;
        case 2:
            printf("This is subtraction: %d\n", b-c);
            b = b-c;
            break;
        case 3:
            printf("This is Multiplication: %d\n", b*c);
            b = b*c;
            break;
        case 4:
            printf("This is division: %d\n", b/c);
            b = b/c;
            break;
        default:
            printf("Oops! Seems like you entered wrong option, Select Again!");
            goto Restart;
    }
    //Check if User want to continue with previous result or not
    printf("Do you want to continue?\n1: Yes\t\t2: No!\n");
    printf("\nChoose option:");
    scanf("%d",&d);
    if (d==1){
        goto Restart;
    }
    else {
        printf("\nThank You! For using the calculator.");
    }
    return 0;
}