Code crashes after scanf in while loop

The problem is in this function. It's supposed to validate input for two variables as integers. What did I do wrong? O__O Thanks :)

I used an if else statement to check for change in the variable valid so that it will exit the loop once the right input is given. Even if I input the right values, the code still crashes.

void input(int *n1, int *n2, char *opt)
{
    int valid = 0;
    int v2 = 0;
    char choice;
    int a, b;


    while (v2  == 0)
    {
        printf("Enter first number: \n");
        if(scanf("%d", &a) == 1)
        {
            while(v2 == 0)
            {
                printf("Enter second number: \n");
                if(scanf("%d", &b) == 1)

                {
                    v2 =1;
                    getchar();
                }
                else
                {
                    getchar();
                    printf("Invalid input!\n");
                }
            }
getchar();          
        }
        else
        {
            getchar();
            printf("Invalid input!\n");
        }
    }



    while( valid == 0)
    {
        printf("Addition -> 1\nSubtraction -> 2\nMultiplication -> 3\nDivision -> 4\nReset -> R\nExit -> E\n");
        scanf("%c", &choice);
        if (choice == 'r' || choice == 'e')
        {
            choice = toupper(choice);
        }
        if ((choice  == '1') ||  (choice  == '2') ||  (choice  == '3') ||  (choice  == '4') ||  (choice  == 'R') ||  (choice  == 'E'))  
        {
            valid = 1;
        }
        else
        {
            printf("Invalid input!\n\n");
        }
    }
    *opt = choice;
    *n1  = a;
    *n2  = b;
}

Here's the whole code for reference. The answers earlier were able to fix the crash. Now, either the loop doesn't exit or it doesn't work right.

#include <stdio.h>
#include <ctype.h>

int add(int n1, int n2);
int subtract(int n1, int n2);
int multiply(int n1, int n2);
int divide(int n1, int n2);
void input(int *n1, int *n2, char *opt);


int main(void)
{
    int n1, n2, ret;
    char opt;

    start:
    input(&n1, &n2, &opt);

    switch(opt)
{
            case '1': 
                ret = add(n1, n2);
                printf("The sum is %d\n", ret);
                break;
            case '2':
                ret = subtract(n1, n2);
                printf("The difference is %d\n", ret);
                break;
            case '3': 
                ret = multiply(n1, n2);
                printf("The product is %d\n", ret); 
                break;              
            case '4': 
                ret = divide(n1, n2);
                printf("The quotient is %d\n", ret);
                break;
            case 'R':
                goto start;
                break;
            case 'E':
                printf("Goodbye!\n");
                return 0;
                break;
    }
    goto start; 
}


void input(int *n1, int *n2, char *opt)
{
    int valid = 0;
    int v2 = 0;
    char choice;
    int a, b;


    while (v2  == 0)
    {
        printf("Enter first number: \n");
        if(scanf("%d", &a) == 1)
        {
            while(v2 == 0)
            {
                printf("Enter second number: \n");
                if(scanf("%d", &b) == 1)

                {
                    v2 =1;
                    getchar();
                }
                else
                {
                    getchar();
                    printf("Invalid input!\n");
                }
            }
getchar();          
        }
        else
        {
            getchar();
            printf("Invalid input!\n");
        }
    }



    while( valid == 0)
    {
        printf("Addition -> 1\nSubtraction -> 2\nMultiplication -> 3\nDivision -> 4\nReset -> R\nExit -> E\n");
        scanf("%c", &choice);
        if (choice == 'r' || choice == 'e')
        {
            choice = toupper(choice);
        }
        if ((choice  == '1') ||  (choice  == '2') ||  (choice  == '3') ||  (choice  == '4') ||  (choice  == 'R') ||  (choice  == 'E'))  
        {
            valid = 1;
        }
        else
        {
            printf("Invalid input!\n\n");
        }
    }
    *opt = choice;
    *n1  = a;
    *n2  = b;
}


int add(n1, n2)
{
    int result;
    result = (n1+n2);
    return result;
}

int subtract(n1, n2)
{
    int result;
    result = (n1-n2);               
    return result;
}

int divide(n1, n2)
{
    int result;
    result = (n1/n2);
    return result;
}

multiply(n1, n2)
{
    int result;
    result = (n1*n2);
    return result;
}