C Functions

Function Definition and Declaration:

• A function in C consists of a function declaration (prototype) and a function definition.
• The function declaration specifies the function name, return type, and parameter types (if any). It informs the compiler about the existence and signature of the function.
• The function definition contains the actual implementation of the function, including the function body (code).
• Here’s an example of a function declaration and definition:

// Function declaration
int addNumbers(int a, int b);

// Function definition
int addNumbers(int a, int b) {
    int sum = a + b;
    return sum;
}

Calling Functions:

• To use a function, you need to call it from another part of your program.
• Function calls typically include the function name followed by parentheses, which may contain arguments (if any).
• The return value of a function can be assigned to a variable or used directly in expressions.
• Here’s an example of calling the addNumbers() function:

int result = addNumbers(3, 4);
printf("The sum is: %d\n", result);

Function Parameters:

• Functions can have parameters, which allow you to pass values to the function.
• Parameters are specified in the function declaration and definition within parentheses.
• The values passed to the function are called arguments.
• Here’s an example of a function with parameters:

int multiply(int a, int b) {
    int product = a * b;
    return product;
}

Function Return Type:

• The return type of a function specifies the type of value the function returns.
• Functions can have various return types, such as int, float, char, void, etc.
• If a function doesn’t return a value, the return type is void.
• Here’s an example of a function with a return type of float:

float calculateAverage(float a, float b, float c) {
    float average = (a + b + c) / 3;
    return average;
}

Function Call by Value:

• By default, C uses call by value, which means that function arguments are passed as copies of their values.
• Any changes made to the parameter within the function do not affect the original argument.
• Here’s an example illustrating call by value:

void increment(int value) {
    value++;
}

int main() {
    int num = 5;
    increment(num);
    printf("The value is: %d\n", num);  // Output: The value is: 5
    return 0;
}

Function Prototypes:

• Function prototypes allow you to declare a function before its actual definition.
• Prototypes specify the function’s name, return type, and parameter types.
• Prototypes are typically placed in a header file that can be included in multiple source files.
• This enables functions to be defined later in the code but still be usable in other parts of the program.
• Here’s an example of a function prototype:

// Function prototype
int multiply(int a, int b);

int main() {
    int result = multiply(3, 4);
    printf("The product is: %d\n", result);
    return 0;
}

// Function definition
int multiply(int a, int b) {
    int product = a * b;
    return product;
}