C Primer Plus, Fourth Edition

String to Number Conversions

Numbers can be stored either as strings or in numeric form. Storing a number as a string means storing the digit characters. For example, the number 213 can be stored in a character string array as the digits '2', '1', '3', '\0'. Storing 213 in numeric form means storing it as, say, an int.

C requires numeric forms for numeric operations, such as addition and comparison, but displaying numbers on your screen requires a string form because a screen displays characters. The printf() and sprintf() functions, through their %d and other specifiers, convert numeric forms to string forms and vice versa. C also has functions whose sole purpose is to convert string forms to numeric forms.

Suppose, for example, that you want ...