Thread: Beginner C problem

Code:

int main() {
    double firstInputCheck = 0;
    double MoneyEachMonth;
    char firstInputNewLine = '?';
    
    while (true) {
        if (firstInputCheck == 0 || firstInputNewLine != '\n' ) {
            printf("Enter how much money you will be putting towards loans/retirement each month: ");
            firstInputCheck = scanf(" %lf", &MoneyEachMonth);
            scanf("%c", &firstInputNewLine);
        } else {
            break;
        }
    }
}

When I try to put in an incorrect input (like bob) it proceeds to print the printf statement 3 times instead of just once.

Recheck the docs on scanf, your using the output wrong if memory serves me correctly

When data on a stream cannot be converted it stays in the stream buffer. When you type 'bob' scanf() will return 0 and "bob\n" will stay in the stdin's buffer... the latter scanf() will read 1 char leaving "ob\n" in the buffer... In the next iteration, "ob" will cause scanf() to fail and the latter scanf() will leave "b\n"... Third interation: scanf() will fail and the second scanf() will get it, leavind only '\n' on buffer.

Probably is best to do something like this:

Code:

char buffer[1024];
double value;
int valid=0;

while ( ! valid )
{
  printf( "Enter value: " ); 
  fflush( stdout );  // to garantee stdout buffer flushing.

  if ( fgets( buffer, sizeof buffer, stdin ) )
    valid = sscanf( buffer, "%lf", &value ) == 1;
}