Example of Switch & Nested Switch: C Programming

Example of Switch & Nested Switch: C Programming
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#include<stdio.h>

int main()
{
    int phn_num, cs;
    printf("Input your phone number: ");
    scanf("%d", &phn_num);
    start:
    printf("\nSelect option\n1.Own Service.\n2.Package.\n3.Call a friend.\n>");
    scanf("%d", &cs);

    switch(cs)
    {
    case 1:
        printf("1.Know your phone number.\n2.Goto main menu.\n>");
        scanf("%d", &cs);
        switch(cs)
        {
        case 1:
            printf("Your phone number is: %d\n", phn_num);
            goto start;
            break;
        case 2:
            goto start;
            break;
        default:
            printf("Error!\n");
            goto start;
        }
        break;

    case 2:
        printf("1.100 SMS.\n2.Talktime\n3.Goto main menu.\n>");
        scanf("%d", &cs);
        switch(cs)
        {
        case 1:
            printf("You brought 100 SMS\n");
            goto start;
            break;
        case 2:
            printf("You brought Talktime\n");
            goto start;
            break;

        case 3:
            goto start;
            break;

        default:
            printf("Error!\n");
            goto start;
        }
        break;
    case 3:
        printf("1.Call X.\n2. Call Y\n3.Goto main menu.\n>");
        scanf("%d", &cs);
        switch(cs)
        {
        case 1:
            printf("You called X\n");
            goto start;
            break;

        case 2:
            printf("You called Y\n");
            goto start;
            break;
        case 3:
            goto start;
            break;
        default:
            printf("Error!\n");
            goto start;

        }
        break;

    default:
        printf("Error!\n");
        goto start;

    }


    return 0;
}