Я думаю, что проблема начинается перед вложенным переключателем if, потому что в конце кода он должен вывести результат sales = quantity * price и change = payment - total amount и запросить quantity и Payment
#include<stdio.h>
main() {
int choice,ch,Quantity,Payment;
printf(" SELECT 1 OPPO \n SELECT 2 SAMSUNG \n SELECT 3 HUAWEI \n\n\n CHOICE: ");
scanf("%d",&choice);
switch(choice){
case 1:
printf("\n OPPO!!!");
printf("\n\nSelect 1 oppo F11 \n Select 2 OPPO A5S \n select 3 OPPO F9 PRO \n\n CHOICE: ");
scanf("%d",&ch);
switch(ch){
case 1:
printf("\n Oppo F11 smartphone was launched in March 2019. The phone comes with a 6.50-inch touchscreen display.\n");
printf("\n P 18,990.00");
break;
case 2:
printf("\n Oppo A5s is built quite sturdily and feels light in hand considering its large footprint.\n");
printf("\n P 6,990.00");
break;
case 3:
printf("\n Oppo F9 Pro features a dual rear camera setup.\n");
printf("\n P 15,990.00");
break;
}
break;
case 2:
printf("\n SAMSUNG!!!");
printf("\n\nSelect 1 SAMSUNG GALAXY A10\n Select 2 SAMSUNG NOTE 10\n select 3 SAMSUNG S9\n\nCHOICE: ");
scanf("%d",&ch);
switch(ch){
case 1:
printf("\n SAMSUNG Galaxy A10 is not a light smartphone, but it is also rather large, making its heft appropriate at least.\n");
printf("\n P 6,990.00");
break;
case 2:
printf("\n The Galaxy Note 10 is Samsung’s easiest to use S Pen-toting phone yet, and while there may not be any game-changing features to make this a must-buy handset, it’s a solid addition to the Note range.\n");
printf("\n P 53,990.00");
break;
case 3:
printf("\n The Samsung Galaxy S9 features a 12MP rear camera with dual-aperture technology. This is the big takeaway from the S9.\n");
printf("\n P 45,990.00");
break;
}
break;
case 3:
printf("\nHUAWEI!!!");
printf("\n\nSelect 1 HUAWEI P30 \n Select 2 HUAWEI NOVA 5T \n select 3 HUAWEI NOVA 3I\n\n CHOICE: ");
scanf("%d",&ch);
switch(ch){
case 1:
printf("\n The Huawei P30 has one of the best cameras we've seen in a phone, with features like incredible optical zoom and night mode that other handsets could only dream of, but other than that it feels more like a decent mid-range handset than a flagship.\n");
printf("\n P 50,990.00");
break;
case 2:
printf("\n Hiding the front camera beneath the screen, HUAWEI nova 5T’s screen retains its full integrity, revolutionizing user experience.\n");
printf("\n P 14,990.00");
break;
case 3:
printf(" \n HUAWEI nova 3i provides three color models for you to choose from, Pearl White, Black and Iris Purple. With beautiful hues of color on the back glass and metal mid-frame, you will enjoy wonderful visual and handling experience.\n");
printf("\n P 14,990.00");
break;
}
break;
default:
printf("\n TRY AGAIN CHOOSE YOUR PHONE BRAND WISELY!!!");
}
scanf("%d", &quantity);
total Amount = quantity * price;
scanf("%d", &payment);
scanf("change = Payment - total Amount);
getch();
}