C++ Programming Default Arguments (Parameters)

C++ Programming Default Arguments (Parameters)

C++ Default Arguments: In this tutorial, we will learn C++ default arguments and their working with the help of examples.

In C++ programming, we can provide default values to function parameters.

If a function with default contentions is called without passing contentions, at that point the default parameters are used.

In any case, if contentions are passed while calling the capacity, the default arguments are ignored.

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Working of default arguments

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We can understand the working of default arguments from the image above:

1. When temp() is called, both the default parameters are used by the function.
2. When temp(6) is called, the first argument becomes 6 while the default value is used for the second parameter.
3. When temp(6, -2.3) is called, both the default parameters are overridden, resulting in i = 6 and f = -2.3.
4. When temp(3.4) is passed, the function behaves in an undesired way because the second argument cannot be passed without passing the first argument.

Therefore, 3.4 is passed as the first argument. Since the first argument has been defined as int, the value that is actually passed is 3.

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Example: Default Argument

#include <iostream>
using namespace std;

// defining the default arguments
void display(char = '*', int = 3);

int main() {
    int count = 5;

    cout << "No argument passed: ";
    // *, 3 will be parameters
    display(); 
    
    cout << "First argument passed: ";
     // #, 3 will be parameters
    display('#'); 
    
    cout << "Both arguments passed: ";
    // $, 5 will be parameters
    display('$', count); 

    return 0;
}

void display(char c, int count) {
    for(int i = 1; i <= count; ++i)
    {
        cout << c;
    }
    cout << endl;
}

Output

No argument passed: ***
First argument passed: ###
Both arguments passed: $$$$$

Here is how this program works:

1. display() is called without passing any arguments. In this case, display() uses both the default parameters c = ‘*’ and n = 1.
2. display(‘#’) is called with only one argument. In this case, the first becomes ‘#’. The second default parameter n = 1 is retained.
3. display(‘#’, count) is called with both arguments. In this case, default arguments are not used.

We can likewise characterize the default boundaries in the capacity definition itself. The program beneath is proportionate to the one above.

#include <iostream>
using namespace std;

// defining the default arguments
void display(char c = '*', int count = 3) {
    for(int i = 1; i <= count; ++i) {
        cout << c;
    }
    cout << endl;
}

int main() {
    int count = 5;

    cout << "No argument passed: ";
    // *, 3 will be parameters
    display(); 
    
    cout << "First argument passed: ";
     // #, 3 will be parameters
    display('#'); 
    
    cout << "Both argument passed: ";
    // $, 5 will be parameters
    display('$', count); 

    return 0;
}

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Things to Remember

1. When we give a default an incentive to a parameter, all resulting boundaries should likewise have default esteems. For instance,

// Invalid
void add(int a, int b = 3, int c, int d);

// Invalid
void add(int a, int b = 3, int c, int d = 4);

// Valid
void add(int a, int c, int b = 3, int d = 4);

2. If we are characterizing the default contentions in the capacity definition rather than the capacity model, at that point the capacity must be characterized before the function call.

// Invalid code

int main() {
    // function call
    display();
}

void display(char c = '*', int count = 5) {
    // code
}

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Please feel free to give your comment if you face any difficulty here.

C++ Functions