There may be a situation, when you need to execute a block of code
several number of times. In general statements are executed
sequentially: The first statement in a function is executed first,
followed by the second, and so on.
Programming languages provide various control structures that allow for more complicated execution paths.
A loop statement allows us to execute a statement or group of
statements multiple times and following is the general from of a loop
statement in most of the programming languages:
C++ programming language provides the following types of loop to
handle looping requirements. Click the following links to check their
detail.
| Loop Type | Description |
|---|
| while loop | Repeats
a statement or group of statements while a given condition is true. It
tests the condition before executing the loop body. |
| for loop | Execute a sequence of statements multiple times and abbreviates the code that manages the loop variable. |
| do...while loop | Like a while statement, except that it tests the condition at the end of the loop body |
| nested loops | You can use one or more loop inside any another while, for or do..while loop. |
Loop Control Statements:
Loop control statements change execution from its normal sequence.
When execution leaves a scope, all automatic objects that were created
in that scope are destroyed.
C++ supports the following control statements. Click the following links to check their detail.
| Control Statement | Description |
|---|
| break statement | Terminates the loop or switch statement and transfers execution to the statement immediately following the loop or switch. |
| continue statement | Causes the loop to skip the remainder of its body and immediately retest its condition prior to reiterating. |
| goto statement | Transfers control to the labeled statement. Though it is not advised to use goto statement in your program. |
The Infinite Loop:
A loop becomes infinite loop if a condition never becomes false. The
for
loop is traditionally used for this purpose. Since none of the three
expressions that form the for loop are required, you can make an endless
loop by leaving the conditional expression empty.
#include <iostream>
using namespace std;
int main ()
{
for( ; ; )
{
printf("This loop will run forever.\n");
}
return 0;
}
When the conditional expression is absent, it is assumed to be true.
You may have an initialization and increment expression, but C++
programmers more commonly use the for(;;) construct to signify an
infinite loop.
NOTE: You can terminate an infinite loop by pressing Ctrl + C keys.
C++ decision making statements
Decision making structures require that the programmer specify one or
more conditions to be evaluated or tested by the program, along with a
statement or statements to be executed if the condition is determined to
be true, and optionally, other
statements to be executed if the condition is determined to be false.
Following is the general from of a typical decision making structure found in most of the programming languages:
C++ programming language provides following types of decision making
statements. Click the following links to check their detail.
| Statement | Description |
|---|
| if statement | An if statement consists of a boolean expression followed by one or more statements. |
| if...else statement | An if statement can be followed by an optional else statement, which executes when the boolean expression is false. |
| switch statement | A switch statement allows a variable to be tested for equality against a list of values. |
| nested if statements | You can use one if or else if statement inside another if or else if statement(s). |
| nested switch statements | You can use one swicth statement inside another switch statement(s). |
The ? : Operator:
We have covered
conditional operator ? : in previous chapter which can be used to replace
if...else statements. It has the following general form:
Exp1 ? Exp2 : Exp3;
Where Exp1, Exp2, and Exp3 are expressions. Notice the use and placement of the colon.
The value of a ? expression is determined like this: Exp1 is
evaluated. If it is true, then Exp2 is evaluated and becomes the value
of the entire ? expression. If Exp1 is false, then Exp3 is evaluated and
its value becomes the value of the expression.
C++ Functions
A function is a group of statements that together perform a task. Every C++ program has at least one function, which is
main(), and all the most trivial programs can define additional functions.
You can divide up your code into separate functions. How you divide
up your code among different functions is up to you, but logically the
division usually is so each function performs a specific task.
A function
declaration tells the compiler about a function's name, return type, and parameters. A function
definition provides the actual body of the function.
The C++ standard library provides numerous built-in functions that your program can call. For example, function
strcat() to concatenate two strings, function
memcpy() to copy one memory location to another location and many more functions.
A function is knows as with various names like a method or a sub-routine or a procedure etc.
Defining a Function:
The general form of a C++ function definition is as follows:
return_type function_name( parameter list )
{
body of the function
}
A C++ function definition consists of a function header and a function body. Here are all the parts of a function:
- Return Type: A function may return a value. The return_type
is the data type of the value the function returns. Some functions
perform the desired operations without returning a value. In this case,
the return_type is the keyword void.
- Function Name: This is the actual name of the function. The function name and the parameter list together constitute the function signature.
- Parameters: A parameter is like a placeholder. When a
function is invoked, you pass a value to the parameter. This value is
referred to as actual parameter or argument. The parameter list refers
to the type, order, and number of the parameters of a function.
Parameters are optional; that is, a function may contain no parameters.
- Function Body: The function body contains a collection of statements that define what the function does.
Example:
Following is the source code for a function called
max(). This function takes two parameters num1 and num2 and returns the maximum between the two:
// function returning the max between two numbers
int max(int num1, int num2)
{
// local variable declaration
int result;
if (num1 > num2)
result = num1;
else
result = num2;
return result;
}
Function Declarations:
A function
declaration tells the compiler about a function
name and how to call the function. The actual body of the function can
be defined separately.
A function declaration has the following parts:
return_type function_name( parameter list );
For the above defined function max(), following is the function declaration:
int max(int num1, int num2);
Parameter names are not importan in function declaration only their type is required, so following is also valid declaration:
int max(int, int);
Function declaration is required when you define a function in one
source file and you call that function in another file. In such case,
you should declare the function at the top of the file calling the
function.
Calling a Function:
While creating a C++ function, you give a definition of what the
function has to do. To use a function, you will have to call or invoke
that function.
When a program calls a function, program control is transferred to
the called function. A called function performs defined task and when
its return statement is executed or when its function-ending closing
brace is reached, it returns program control back to the main program.
To call a function, you simply need to pass the required parameters
along with function name, and if function returns a value, then you can
store returned value. For example:
#include <iostream>
using namespace std;
// function declaration
int max(int num1, int num2);
int main ()
{
// local variable declaration:
int a = 100;
int b = 200;
int ret;
// calling a function to get max value.
ret = max(a, b);
cout << "Max value is : " << ret << endl;
return 0;
}
// function returning the max between two numbers
int max(int num1, int num2)
{
// local variable declaration
int result;
if (num1 > num2)
result = num1;
else
result = num2;
return result;
}
I kept max() function along with main() function and compiled the
source code. While running final executable, it would produce the
following result:
Max value is : 200
Function Arguments:
If a function is to use arguments, it must declare variables that
accept the values of the arguments. These variables are called the
formal parameters of the function.
The formal parameters behave like other local variables inside the
function and are created upon entry into the function and destroyed upon
exit.
While calling a function, there are two ways that arguments can be passed to a function:
| Call Type | Description |
|---|
| Call by value | This
method copies the actual value of an argument into the formal parameter
of the function. In this case, changes made to the parameter inside the
function have no effect on the argument. |
| Call by pointer | This
method copies the address of an argument into the formal parameter.
Inside the function, the address is used to access the actual argument
used in the call. This means that changes made to the parameter affect
the argument. |
| Call by reference | This
method copies the reference of an argument into the formal parameter.
Inside the function, the reference is used to access the actual argument
used in the call. This means that changes made to the parameter affect
the argument. |
By default, C++ uses
call by value to pass arguments. In
general, this means that code within a function cannot alter the
arguments used to call the function and above mentioned example while
calling max() function used the same method.
Default Values for Parameters:
When you define a function, you can specify a default value for each
of the last parameters. This value will be used if the corresponding
argument is left blank when calling to the function.
This is done by using the assignment operator and assigning values
for the arguments in the function definition. If a value for that
parameter is not passed when the function is called, the default given
value is used, but if a value is specified, this default value is
ignored and the passed value is used instead. Consider the following
example:
#include <iostream>
using namespace std;
int sum(int a, int b=20)
{
int result;
result = a + b;
return (result);
}
int main ()
{
// local variable declaration:
int a = 100;
int b = 200;
int result;
// calling a function to add the values.
result = sum(a, b);
cout << "Total value is :" << result << endl;
// calling a function again as follows.
result = sum(a);
cout << "Total value is :" << result << endl;
return 0;
}
When the above code is compiled and executed, it produces the following result:
Total value is :300
Total value is :120
Numbers in C++
Normally, when we work with Numbers, we use primitive data types such
as int, short, long, float and double, etc. The number data types,
their possible values and number ranges have been explained while
discussing C++ Data Types.
Defining Numbers in C++:
You have already defined numbers in various examples given in
previous chapters. Here is another consolidated example to define
various types of numbers in C++:
#include <iostream>
using namespace std;
int main ()
{
// number definition:
short s;
int i;
long l;
float f;
double d;
// number assignments;
s = 10;
i = 1000;
l = 1000000;
f = 230.47;
d = 30949.374;
// number printing;
cout << "short s :" << s << endl;
cout << "int i :" << i << endl;
cout << "long l :" << l << endl;
cout << "float f :" << f << endl;
cout << "double d :" << d << endl;
return 0;
}
When the above code is compiled and executed, it produces the following result:
short s :10
int i :1000
long l :1000000
float f :230.47
double d :30949.4
Math Operations in C++:
In addition to the various functions you can create, C++ also
includes some useful functions you can use. These functions are
available in standard C and C++ libraries and called
built-in functions. These are functions that can be included in your program and then use.
C++ has a rich set of mathematical operations, which can be performed
on various numbers. Following table lists down some useful built-in
mathematical functions available in C++.
To utilize these functions you need to include the math header file
<cmath>.
| S.N. |
Function & Purpose |
| 1 |
double cos(double);
This function takes an angle (as a double) and returns the cosine.
|
| 2 |
double sin(double);
This function takes an angle (as a double) and returns the sine.
|
| 3 |
double tan(double);
This function takes an angle (as a double) and returns the tangent.
|
| 4 |
double log(double);
This function takes a number and returns the natural log of that number.
|
| 5 |
double pow(double, double);
The first is a number you wish to raise and the second is the power you wish to raise it t
|
| 6 |
double hypot(double, double);
If you pass this function the length of two sides of a right triangle, it will return you the length of the hypotenuse.
|
| 7 |
double sqrt(double);
You pass this function a number and it gives you this square root.
|
| 8 |
int abs(int);
This function returns the absolute value of an integer that is passed to it.
|
| 9 |
double fabs(double);
This function returns the absolute value of any decimal number passed to it.
|
| 10 |
double floor(double);
Finds the integer which is less than or equal to the argument passed to it.
|
Following a simple example to show few of the mathematical operations:
#include <iostream>
#include <cmath>
using namespace std;
int main ()
{
// number definition:
short s = 10;
int i = -1000;
long l = 100000;
float f = 230.47;
double d = 200.374;
// mathematical operations;
cout << "sin(d) :" << sin(d) << endl;
cout << "abs(i) :" << abs(i) << endl;
cout << "floor(d) :" << floor(d) << endl;
cout << "sqrt(f) :" << sqrt(f) << endl;
cout << "pow( d, 2) :" << pow(d, 2) << endl;
return 0;
}
When the above code is compiled and executed, it produces the following result:
sign(d) :-0.634939
abs(i) :1000
floor(d) :200
sqrt(f) :15.1812
pow( d, 2 ) :40149.7
Random Numbers in C++:
There are many cases where you will wish to generate a random number.
There are actually two functions you will need to know about random
number generation. The first is
rand(), this function will only return a pseudo random number. The way to fix this is to first call the
srand() function.
Following is a simple example to generate few random numbers. This example makes use of
time() function to get the number of seconds on your system time, to randomly seed the rand() function:
#include <iostream>
#include <ctime>
#include <cstdlib>
using namespace std;
int main ()
{
int i,j;
// set the seed
srand( (unsigned)time( NULL ) );
/* generate 10 random numbers. */
for( i = 0; i < 10; i++ )
{
// generate actual random number
j= rand();
cout <<" Random Number : " << j << endl;
}
return 0;
}
When the above code is compiled and executed, it produces the following result:
Random Number : 1748144778
Random Number : 630873888
Random Number : 2134540646
Random Number : 219404170
Random Number : 902129458
Random Number : 920445370
Random Number : 1319072661
Random Number : 257938873
Random Number : 1256201101
Random Number : 580322989
