Binary numbers are seldom implemented in Visual C++ applications because C++ is considered a "high-level" language. Yet in communications systems, where information is transferred between two different devices through a network, using binary or hexadecimal numbers is much easier than decimal numbers.

In some applications, the computer's user interface will guide the user to input a hexadecimal number via the keyboard. Because this number will be transferred to an embedded system, it must be converted to a "real" number before leaving the PC. In this case, the hexadecimal-number data type in-putted by the user is string. Unfortunately, Visual C++ 6.0 doesn't offer a conversion function that can transform a string (representing a hexadecimal number) into a real hexadecimal or binary number.

The program to execute such a function implements the flow chart shown in the figure. You must first translate the inputted hexadecimal string into a binary string. Because a hexadecimal character represents a 4-bit binary number, it's better to employ a "switch case" structure to convert a hexadecimal character to a 4-bit binary string. Function *convert_hex2bin()* carries out this conversion.

After converting the whole hexadecimal string into a binary string, you must translate every 4-bit binary string into an integer that represents the real value of the 4-bit binary number. Function *convert_sbin2int() *returns this integer value. In this function, the binary string is transformed into a real integer by subfunction *atoi()*, which is included in the VC++ IDE. This "binary" integer is then converted into a decimal. Finally, all of the small integers are accumulated to form the final result. The resulting real number can be sent to an embedded system or be displayed on the screen as a decimal number.

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