Code:
if (input[idx] < 48 || input[idx] > 57)
I find '0' clearer than 48.

Code:
{	// this whole code block is useless

            char ch;
	char input[10];
	int idx, decimal_found ;

	}
	printf("\n\n Please enter a dollar amount you would like to convert. (US Dollars): ");
	scanf("%f",&money);

    // somewhere in here you should actually read something into input
	
	decimal_found = 0 ;

	/*Checks for validity of input entered by user for numerical value,retreived from Aruna Pandey*/
 	for (idx = 0 ; idx < strlen(input) ; idx++)  // input is not initialized!
        {
            if (input[idx] == '.')
            {
And, as someone mentioned, get rid of the fflush(stdin).