What are different between declaration & definition?

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Declaration means defining the variable or function. Definition means group of instruction or group of statement to be performed when function is call. It defined the task of function.
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A declaration introduces an identifier and describes its type, be it a type, object, or function. A declaration is what the compiler needs to accept references to that identifier. These are declarations: extern int bar; extern int g(int, int); double f(int, double); // extern can be omitted for...
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A declaration introduces an identifier and describes its type, be it a type, object, or function. A declaration is what the compiler needs to accept references to that identifier. These are declarations: extern int bar; extern int g(int, int); double f(int, double); // extern can be omitted for function declarations class foo; // no extern allowed for type declarations A definition actually instantiates/implements this identifier. It's what the linker needs in order to link references to those entities. These are definitions corresponding to the above declarations: int bar; int g(int lhs, int rhs) {return lhs*rhs;} double f(int i, double d) {return i+d;} class foo {}; A definition can be used in the place of a declaration. An identifier can be declared as often as you want. Thus, the following is legal in C and C++: double f(int, double); double f(int, double); extern double f(int, double); // the same as the two above extern double f(int, double); read less
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Declaration tells the compiler the presence of a variable named so and so in the program. Definition assigns the memory address to the variable. The best example of declaration and definition is: struct var { int a; char b; }; This is only declaration because no object is created of var type. Whereas,...
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Declaration tells the compiler the presence of a variable named so and so in the program. Definition assigns the memory address to the variable. The best example of declaration and definition is: struct var { int a; char b; }; This is only declaration because no object is created of var type. Whereas, If we do int x; in main() function, then it is declaration and definition as well because compiler gets to know about x and memory location is also assigned to x. read less
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Thanks for the question Rajinder...... Declaring a variable means to inform the compiler that the variable is declared of this data type. Variable definition means to ask the compiler for memory. Thanks, Team DishaaPro www.dishaapro.com
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