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Functions (i.e., methods) in C

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• Defining functions
  • Syntax of C function definition:

    return-Type functionName ( formal-parameters ) { function-body (local variables and statements) }

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  • The function definition is stored in a file and it is not contained inside any structure

    Example:

    float square( float x ) { float r; // Define a local variable r = x * x; // Statement return ( r ); // Return statement }

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• Warning: C is not object-oriented !!!
  • Recall that:

    C is not an object oriented programming language Only object oriented programming languages have instance methods Recall that instance methods have an implicit parameter (called this) All programming languages have class methods Recall that class methods only have explicit parameter (that appear between the brackets after the name of the function)

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  • Therefore:

    The functions in C are comparable to the class methods in Java: Functions in C do not have any implicit parameter (this) All parameters of a function appear between the brackets after the name of the function.

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• Calling (using) a (previously defined) function
  • Syntax to invoke a (previously defined) function:

    functionName ( actual-parameters ) // if function does not return any value or: var = functionName ( actual-parameters ) // if function returns a value

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  • Example:

    #include <stdio.h> float square( float x ) { float r; // Define a local variable r = x * x; // Statement return ( r ); // Return statement } int main( int argc, char *argv[] ) { float a, b; a = 4.0; b = square( a ); // Call function square printf("a = %f, b = %f\n", a, b); }

    Output:

    a = 4.000000, b = 16.000000

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  • Example Program: (Demo above code)                                                
    • Prog file: /home/cs255001/demo/C/set1/func1.c

    How to run the program:

    To compile:   gcc func1.c          To run: ./a.out