Objective-C is an object-oriented programming language that adds another programming language’s Smalltalk-style syntax to the C programming language.
These days, it is used primarily for Apple’s Mac and iPhone based iOS development. Objective-C is a thin layer on top of C, and is a strict superset of C. It is possible to compile any C program with an Objective-C compiler, and also to freely include C code within an Objective-C class.
Objective-C object syntax is based on another programming language Smalltalk. All of the syntax for non-object-oriented operations (including primitive variables, preprocessing, expressions, function declarations, and function calls) are identical to that of C, while the syntax for object-oriented features is similar to Smalltalk-style messaging.
In this section we shall try to discuss Objective C topics like stringwithformat and hence, slowly move towards iphone development as well.
Another useful resource for learning objective c is linked here.