Elements of a C Program

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Elements of a C Program
ECOR 1606 - Problem Solving and Computers
Carleton University Department of Systems and
Computer Engineering
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Elements of a simple program

• Comments
• meant for the human reader
• ignored by the compiler
• can be placed anywhere in the program
• two methods for comments
• / ignore everything in between /
• // ignore until the end of the line

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Elements of a simple program

• Include directives
• include ltfilenamegt
• tells compiler to read the specified header file
• enables optional features
• permits access to library functions
• examples of standard header files
• iostream cin, cout
• cmath pow(), exp(), sin(), sqrt( )
• cstdlib rand(), qsort(), getcwd( )

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Elements of a simple program

• Main function
• tells the compiler that your actual program
  starts here
• basically, this is the name of the function that
  the operating system calls to begin running your
  program
• this function must be called main

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Elements of a simple program

• Declarations
• specifies the names and types of variables that
  will be used
• examples
• int x
• double y

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Elements of a simple program

• Executable Statements
• the actual instructions for the algorithm
• examples
• cout ltlt "Hello, World!"
• x 10 y
• z sqrt(17.2)

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Hello, World! Program
/ Print "Hello, World!", then exit.
/ include ltiostreamgt // for cout using
namespace std int main() cout ltlt "Hello,
World!" ltlt endl system("PAUSE") return
0
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Average Value Program
comment
/ Read in three numbers and print their
average value / include ltiostreamgt using
namespace std int main() double
value1, value2, value3, average cout ltlt
"Enter three numbers " cin gtgt value1 gtgt
value2 gtgt value3 average (value1
value2 value3) / 3 cout ltlt "The
average is " ltlt average ltlt endl
system("PAUSE") return 0
include directives
declarations
main function
print prompt
read values
calculate average
print result
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User Window

• Program output (shown here in black) the
  content of the output stream produced by the
  statements of the form cout ltlt . . .
• Program input (shown here in red) the content of
  the input stream entered by the user and
  processed by the statements cin gtgt . . .