C language doesn't scan variable

C language doesn’t scan variable after reading that variable as string(or char) instead of integer
But the most weird is that it is entering in infinite loop

int main( ){
    int answer;
    printf("Hello\n");

    while (answer != 3){
        start();//It is declared above
        scanf("%d",&answer);
        switch (answer) {
            case 1:{
                showCenters();//Also declared
                break;}
            case 3:{
                break;}
            default:{
                printf("Invalid input\nTry again\n\n");
                break;}
        }
    }

    return 0;
}

To find how C language works and fix the problem

>Solution :

You can add one more statement under the label default to avoid an infinite loop when a non-number is entered

        default: {
            printf( "Invalid input\nTry again\n\n" );
            scanf( "%*[^\n]" );
            break; }
        }

If the user will try to interrupt the input you can also write

if ( scanf("%d",&answer) == EOF ) break;

to exit the while loop.

Pay attention to that the variable answer shall be initialized before the while loop.