Dynamic Memory&

File Input/Output

Dynamic Memory: Introduction

• Generally the memory requirements of a program are determined before program execution by the declaration of variables.

• In this way the program will always use the same amount of memory and this cannot be changed while the program is running.

• It is generally useful however to adjust the memory requirements at runtime especially when your program needs a user input to determine the number of variables.

Dynamic Memory: Introduction

• The allocation of memory at runtime is referred to as dynamic memory allocation.

• Dynamic memory allocation is managed in C++ using the new and delete keywords.

• The new keyword is used to dynamically allocate memory for variables and the delete keyword is used to release that memory when it is no longer needed.

Dynamic Memory: Basic Syntax• When dynamic memory is created a pointer to

that memory location is what is returned to the program.

• To use the new keyword to dynamically allocate memory the following syntax is used:

pointer = new type;pointer = new type [number_of_elements];

• The first statement creates one variable and the second creates an array of variables.

Dynamic Memory: Example• The dynamic array is the more useful an

example is: int *foo; int lent=0; cout<<"please enter a length: "; cin>>lent; foo=new int[lent]; //dynamic array created cout<<"please enter numbers: "; for (int cnt=0;cnt<lent;cnt++) { cin>>foo[cnt]; //or cin>>*(foo+cnt); }

Dynamic Memory: Class Exercise

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File Input/Output: Introduction

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File Input/Output: Introduction

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File Input/Output: Basic Syntax

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File Input/Output: Basic Syntax

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File Input/Output: Basic Syntax•

File Input/Output: Basic Syntax

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File Input/Output: Basic Syntax

• We will work mostly with text files so the output to them will be formatted as text. This is much the same way that the standard output stream works.

• Once opened a file object is written to like the standard input/output.

File Input/Output: Example

File Input/Output: Basic Syntax

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File Input/Output: Basic Syntax

Class Exercise

• Create a program to find the average of a group of numbers and print the numbers and their average.

• The numbers and their average should also be saved to a file.

• The amount of numbers must be specified by the user at runtime.

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