A.Aminian - CFD Group (Supervisor: Dr. Mohsen Lahooti)

1. Functions in C++
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2. Section Outline
• Definition of a function
• Calling function
• Recursive functions
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3. Section Outline
• Definition of a function
• Calling function
• Recursive functions
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4. Definition of a function
• Every where in C++ environment we can
define a function
OutPutType name (argument1, argument2, …)
{
…………………………
…………………………
…………………………
return output
}
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This two type must have a
same type

5. Definition of a function(cont.)
• Some note:
Functions in C++ works the same as SUBROUTINs
There is no need to use CONTAINS or any similar
keywords to introduce functions to the program
The main() part of our code must know the
presence of our functions and this possible by a
predefine or define our function the top of main()
(disobey of this rule make a error)
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6. Definition of a function(cont.)
• e.g. (1) : predefine
int MyFuntioin(int);
int main()
{
int t = 12;
int a = MyFunction(t);
return 0;
}
int MyFunction(int q)
{
……..
……..
……..
return f;
}
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• e.g. (2): define
int MyFunction(int q)
{
……..
……..
……..
return f;
}
int main()
{
int t = 12;
int a = MyFunction(t);
return 0;
}

7. Definition of a function(cont.)
• Some notes:
 We can use function`s output like a statement or a variable
• Anywhere in our code, we can define a function such as MyFunction ()
that it`s output is an integer. after that we write the following
command to use the function:
int a = MyFunction();
e.g.
int sub (int a, int b) { return a-b; }
void main() { int a = sub (8,2); return; }
Note: There is no need to use CALL or such key word to call a function,
we just need to write function’s name.
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8. Definition of a function(cont.)
• Some notes(cont.):
If you want to write your own functions into the
other files or headers (instead of the main file),
you must include them just like libraries with “..”:
e.g:
#include “myfunctions.h”
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9. Definition of a function(cont.)
• e.g.(.h and .cpp)
# include “sub.h”
void main()
{
int a = sub(7,2);
cout << a;
}
Note : we use “…” in define include when we create
a header ourselves
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//sub.h
int sub (int , int );
//sub.cpp
# include ”sub.h”
int sub (int a, int b)
{
return a-b;
}

10. Section Outline
• Definition of a function
• Calling Function
• Recursive functions
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11. Calling Function
• Passing parameter
– e.g. int sub (int a, int b, int c)
{ return b-c; }
void main ()
{ cout <<sub(e,g,f); return 0; }
– Arrays
• Because of array`s nature as pointer, we pass an array as a pointer
• Upper dimensions than 1D must introduce to the list of argument
(we can introduce all dimensions to the function)
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12. Calling Function(cont.)
• e.g.
int array _based _function ( int * first , int second[][5])
{…………………….}
int main ()
{
int a[100], b[100][5];
return array _based _function (a, b);
}
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int first[]int first[100]

13. Calling Function(cont.)
• We have two types of calling function
1. Calling by value
2. Calling by references
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14. Calling Function(cont.)
1. Calling by value
e.g.
int cubeValue(int n)
{
return n*n*n;
}
int main()
{
int number = 5;
number = cubeValue(5);
return 0;
}
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int cubeValue ( int n)
{
int f = n*n*n;
return f;
}

15. Calling Function(cont.)
2. Calling by references
e.g.
void cubeValue(int * n)
{
*n = *n * *n * *n;
}
int main()
{
int number = 5;
number = cubeValue(& number);
return 0;
}
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16. Some Important Functions
• List of some computational functions:
• Note: You must include the math library in order to use them.
#include <math>
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Mathematical def. C++ Fortran
sqrt(x) SQRT(X)
exp(x) exp(x) EXP(X)
ln(x) ln(x) LOG(X)
log10(x) LOG10(X)
sin(x) sin(x) SIN(X)
cos(x) cos(x) COS(X)
tan(x) tan(x) TAN(X)
Residual x % y MOD(X,Y)
x
10logx

17. Some Important Functions
#include <math>
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Mathematical def. C++ Fortran
sinh(x) sinh(x) SINH(X)
cosh(x) cosh(x) COSH(X)
tanh(x) tanh(x) TANH(X)
sin-1(x) asin(x) ASIN(X)
cos-1(x) acos(x) ACOS(X)
tan-1(x) atan(x) ATAN(X)
|x| labs(x) ABS(X)
[x] floor(x) INT(X)

18. In future :
i. Class and related concepts
ii. ERRORS
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