The parameter type dataType a[ ] and the parameter type dataType *a in C

  • The parameter int a[ ] in a C function represents an array as parameter: 

     void f(int a[ ]) // a is the base address of an array of int variables
 {
    ...
 }

 The parameter a contains the base address of an int typed array:

                  |       |
		  +-------+
	     a:	  |  7000 |
		  +-------+
		  |  ...  |
		  |  ...  |
		  +-------+
	    7000  |  int  | <--- there is an int type array    here
		  +-------+
		  |  int  |
		  +-------+
		  |  int  |
		  +-------+
		  |  ...  |

     

     

The parameter type dataType a[ ] and the parameter type dataType *a in C

  • The parameter int *a in a C function represents an reference variable as parameter: 

     void f(int *a)   // a is the      address of int typed variable
 {
    ...
 }

 The parameter a contains the      address of an int typed variable:

                  |       |
		  +-------+
	     a:	  |  7000 |
		  +-------+
		  |  ...  |
		  |  ...  |
		  +-------+
	    7000  |  int  | <--- there is an int type variable here
		  +-------+
		  |  ???  |
		  +-------+
		  |  ???  |
		  +-------+
		  |  ...  |

    Notice:   there is no difference in the interpretation of int a[ ] and int *a !!!

    In both cases, the parameter a contains the address of an int typed variable !!!

In C: the declaration a[] and the declaration *a are equivalent

  • We have seen that the notation double list[] declares an array of double as parameter: 

        void selectionSort(double list[], int N) 
    {
        for (int k = 0; k < N-1; k++)
        {
            // Find the minimum value and its index in list[k..N-1]
            double min = list[k];    // Assume first element is min
            int    indexOfMin = k;   // Index of current min

            for ( int i = k+1; i < N; i++ )
                if ( list[i] < min ) // We found a smaller element
                {
                    min = list[i];   // Update min value
                    indexOfMin = i;  // Update its index in array
                }
   
            // Swap list[k] with list[indexOfMin] if necessary
            if ( indexOfMin != k )
            {   // Swap list[indexOfMin] and list[k]
                double help = list[indexOfMin];
                list[indexOfMin] = list[k];
                list[k] = help;
            }
        } 
    }

    Notice:   the expression list[k] is using array member selection

In C: the declaration a[] and the declaration *a are equivalent

  • We can also use double *list to declare an array of double as parameter: 

        void selectionSort(double *list, int N) 
    {
        for (int k = 0; k < N-1; k++)
        {
            // Find the minimum value and its index in list[k..N-1]
            double min = list[k];    // Assume first element is min
            int    indexOfMin = k;   // Index of current min

            for ( int i = k+1; i < N; i++ )
                if ( list[i] < min ) // We found a smaller element
                {
                    min = list[i];   // Update min value
                    indexOfMin = i;  // Update its index in array
                }
   
            // Swap list[k] with list[indexOfMin] if necessary
            if ( indexOfMin != k )
            {   // Swap list[indexOfMin] and list[k]
                double help = list[indexOfMin];
                list[indexOfMin] = list[k];
                list[k] = help;
            }
        } 
    }

    Notice:   the expression list[k] is using short hand [ ] with pointer arithmetic

DEMO: demo/C/set1/selectionSort2.c