411 REFERENCE · Wikibooks
C++ Language/Std/Strings/CastingNumericValues/StringToNumber
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
The inverse of formatted-printing can cast from a C-string into a numeric variable: sscanf("11", "&d", &iVar);.
Additional information about casting from string to number (includes interactive examples)