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C++ Programming Code Examples

C++ > Data Structures and Algorithm Analysis in C++ Code Examples

Recursive routine to print numbers, with a test program

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/* Recursive routine to print numbers, with a test program */ #include <iostream.h> void printDigit( int n ) { cout << n; } void printOut( int n ) // Print nonnegative n { if( n >= 10 ) printOut( n / 10 ); printDigit( n % 10 ); } /* END */ int main( ) { printOut( 1369 ); cout << endl; return 0; }
Comments in C++
The C++ comments are statements that are not executed by the compiler. The comments in C++ programming can be used to provide explanation of the code, variable, method or class. If we write comments on our code, it will be easier for us to understand the code in the future. Also, it will be easier for your fellow developers to understand the code. By the help of comments, you can hide the program code also. There are two types of comments in C++: • Single Line comment • Multi Line comment
Syntax for Single Line Comment in C++
/* This is a comment */
The single line comment starts with // (double slash).
Syntax for Multi Line Comment in C++
/* C++ comments can also * span multiple lines */
C++ multi line comment is used to comment multiple lines of code. It is surrounded by slash and asterisk (/* ..... */). Comments shouldn't be the substitute for a way to explain poorly written code in English. We should always write well-structured and self-explanatory code. And, then use comments.
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/* program to illustrate use comments in C++ language */ #include <ostream> using namespace std; int main() { int x = 11; // x is a variable cout<<x<<"\n"; /* declare and print variable in C++ */ int x = 35; cout<<x<<"\n"; // This is a comment cout << "Hello World!"; /* Multi-line Comments in C++ */ }
If Else Statement in C++
In computer programming, we use the if statement to run a block code only when a certain condition is met. An if statement can be followed by an optional else statement, which executes when the boolean expression is false. There are three forms of if...else statements in C++: • if statement, • if...else statement, • if...else if...else statement,
Syntax for If Statement in C++
if (condition) { // body of if statement }
The if statement evaluates the condition inside the parentheses ( ). If the condition evaluates to true, the code inside the body of if is executed. If the condition evaluates to false, the code inside the body of if is skipped.
Syntax for If...Else Statement
if (condition) { // block of code if condition is true } else { // block of code if condition is false }
The if..else statement evaluates the condition inside the parenthesis. If the condition evaluates true, the code inside the body of if is executed, the code inside the body of else is skipped from execution. If the condition evaluates false, the code inside the body of else is executed, the code inside the body of if is skipped from execution. The if...else statement is used to execute a block of code among two alternatives. However, if we need to make a choice between more than two alternatives, we use the if...else if...else statement.
Syntax for If...Else...Else If Statement in C++
if (condition1) { // code block 1 } else if (condition2){ // code block 2 } else { // code block 3 }
• If condition1 evaluates to true, the code block 1 is executed. • If condition1 evaluates to false, then condition2 is evaluated. • If condition2 is true, the code block 2 is executed. • If condition2 is false, the code block 3 is executed. There can be more than one else if statement but only one if and else statements. In C/C++ if-else-if ladder helps user decide from among multiple options. The C/C++ if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the C else-if ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.
Syntax for If Else If Ladder in C++
if (condition) statement 1; else if (condition) statement 2; . . else statement;
Working of the if-else-if ladder: 1. Control falls into the if block. 2. The flow jumps to Condition 1. 3. Condition is tested. If Condition yields true, goto Step 4. If Condition yields false, goto Step 5. 4. The present block is executed. Goto Step 7. 5. The flow jumps to Condition 2. If Condition yields true, goto step 4. If Condition yields false, goto Step 6. 6. The flow jumps to Condition 3. If Condition yields true, goto step 4. If Condition yields false, execute else block. Goto Step 7. 7. Exits the if-else-if ladder. • The if else ladder statement in C++ programming language is used to check set of conditions in sequence. • This is useful when we want to selectively executes one code block(out of many) based on certain conditions. • It allows us to check for multiple condition expressions and execute different code blocks for more than two conditions. • A condition expression is tested only when all previous if conditions in if-else ladder is false. • If any of the conditional expression evaluates to true, then it will execute the corresponding code block and exits whole if-else ladder.
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/* If Else Statement in C++ Language */ #include <iostream> using namespace std; int main () { // local variable declaration: int a = 100; // check the boolean condition if( a < 20 ) { // if condition is true then print the following cout << "a is less than 20;" << endl; } else { // if condition is false then print the following cout << "a is not less than 20;" << endl; } cout << "value of a is : " << a << endl; return 0; }
main() Function in C++
A program shall contain a global function named main, which is the designated start of the program in hosted environment. main() function is the entry point of any C++ program. It is the point at which execution of program is started. When a C++ program is executed, the execution control goes directly to the main() function. Every C++ program have a main() function.
Syntax for main() Function in C++
void main() { ............ ............ }
void
void is a keyword in C++ language, void means nothing, whenever we use void as a function return type then that function nothing return. here main() function no return any value.
main
main is a name of function which is predefined function in C++ library. In place of void we can also use int return type of main() function, at that time main() return integer type value. 1) It cannot be used anywhere in the program a) in particular, it cannot be called recursively b) its address cannot be taken 2) It cannot be predefined and cannot be overloaded: effectively, the name main in the global namespace is reserved for functions (although it can be used to name classes, namespaces, enumerations, and any entity in a non-global namespace, except that a function called "main" cannot be declared with C language linkage in any namespace). 3) It cannot be defined as deleted or (since C++11) declared with C language linkage, constexpr (since C++11), consteval (since C++20), inline, or static. 4) The body of the main function does not need to contain the return statement: if control reaches the end of main without encountering a return statement, the effect is that of executing return 0;. 5) Execution of the return (or the implicit return upon reaching the end of main) is equivalent to first leaving the function normally (which destroys the objects with automatic storage duration) and then calling std::exit with the same argument as the argument of the return. (std::exit then destroys static objects and terminates the program). 6) (since C++14) The return type of the main function cannot be deduced (auto main() {... is not allowed). 7) (since C++20) The main function cannot be a coroutine.
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/* simple code example by main() function in C++ */ #include <iostream> using namespace std; int main() { int day = 4; switch (day) { case 1: cout << "Monday"; break; case 2: cout << "Tuesday"; break; case 3: cout << "Wednesday"; break; case 4: cout << "Thursday"; break; case 5: cout << "Friday"; break; case 6: cout << "Saturday"; break; case 7: cout << "Sunday"; break; } return 0; }
Return Statement in C++
A return statement ends the processing of the current function and returns control to the caller of the function. A value-returning function should include a return statement, containing an expression. If an expression is not given on a return statement in a function declared with a non-void return type, the compiler issues an error message. If the data type of the expression is different from the function return type, conversion of the return value takes place as if the value of the expression were assigned to an object with the same function return type.
Syntax for Return Statement in C++
return[expression];
For a function of return type void, a return statement is not strictly necessary. If the end of such a function is reached without encountering a return statement, control is passed to the caller as if a return statement without an expression were encountered. In other words, an implicit return takes place upon completion of the final statement, and control automatically returns to the calling function. If a return statement is used, it must not contain an expression. The following are examples of return statements:
return; /* Returns no value */ return result; /* Returns the value of result */ return 1; /* Returns the value 1 */ return (x * x); /* Returns the value of x * x */
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/* illustrate Methods returning a value using return statement in C++ code example */ #include <iostream> using namespace std; // non-void return type // function to calculate sum int SUM(int a, int b) { int s1 = a + b; // method using the return // statement to return a value return s1; } // Driver method int main() { int num1 = 10; int num2 = 10; int sum_of = SUM(num1, num2); cout << "The sum is " << sum_of; return 0; }
#include Directive in C++
#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program.
Syntax for #include Directive in C++
#include "user-defined_file"
Including using " ": When using the double quotes(" "), the preprocessor access the current directory in which the source "header_file" is located. This type is mainly used to access any header files of the user's program or user-defined files.
#include <header_file>
Including using <>: While importing file using angular brackets(<>), the the preprocessor uses a predetermined directory path to access the file. It is mainly used to access system header files located in the standard system directories. Header File or Standard files: This is a file which contains C/C++ function declarations and macro definitions to be shared between several source files. Functions like the printf(), scanf(), cout, cin and various other input-output or other standard functions are contained within different header files. So to utilise those functions, the users need to import a few header files which define the required functions. User-defined files: These files resembles the header files, except for the fact that they are written and defined by the user itself. This saves the user from writing a particular function multiple times. Once a user-defined file is written, it can be imported anywhere in the program using the #include preprocessor. • In #include directive, comments are not recognized. So in case of #include <a//b>, a//b is treated as filename. • In #include directive, backslash is considered as normal text not escape sequence. So in case of #include <a\nb>, a\nb is treated as filename. • You can use only comment after filename otherwise it will give error.
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/* using #include directive in C language */ #include <stdio.h> int main() { /* * C standard library printf function * defined in the stdio.h header file */ printf("I love you Clementine"); printf("I love you so much"); printf("HappyCodings"); return 0; }
Relational Operators in C++
A relational operator is used to check the relationship between two operands. C++ Relational Operators are used to relate or compare given operands. Relational operations are like checking if two operands are equal or not equal, greater or lesser, etc. Relational Operators are also called Comparison Operators. • == Is Equal To 4 == 9 gives us false • != Not Equal To 4 != 9 gives us true • > Greater Than 4 > 9 gives us false • < Less Than 4 < 9 gives us true • >= Greater Than or Equal To 4 >= 9 give us false • <= Less Than or Equal To 4 <= 9 gives us true
==
Equal To Operator (==) is used to compare both operands and returns 1 if both are equal or the same, and 0 represents the operands that are not equal. The equal to == operator returns true - if both the operands are equal or the same false - if the operands are unequal int x = 10; int y = 15; int z = 10; x == y // false x == z // true The relational operator == is not the same as the assignment operator =. The assignment operator = assigns a value to a variable, constant, array, or vector. It does not compare two operands.
!=
Not Equal To Operator (!=) is the opposite of the Equal To Operator and is represented as the (!=) operator. The Not Equal To Operator compares two operands and returns 1 if both operands are not the same; otherwise, it returns 0. The not equal to != operator returns true - if both operands are unequal false - if both operands are equal. int x = 10; int y = 15; int z = 10; x != y // true x != z // false
>
Greater than Operator (>) checks the value of the left operand is greater than the right operand, and if the statement is true, the operator is said to be the Greater Than Operator. The greater than > operator returns true - if the left operand is greater than the right false - if the left operand is less than the right int x = 10; int y = 15; x > y // false y > x // true
<
Less than Operator (<) is used to check whether the value of the left operand is less than the right operand, and if the statement is true, the operator is known as the Less than Operator. The less than operator < returns true - if the left operand is less than the right false - if the left operand is greater than right int x = 10; int y = 15; x < y // true y < x // false
>=
Greater than Equal To Operator (>=) checks whether the left operand's value is greater than or equal to the right operand. If the statement is true, the operator is said to be the Greater than Equal to Operator. The greater than or equal to >= operator returns true - if the left operand is either greater than or equal to the right false - if the left operand is less than the right int x = 10; int y = 15; int z = 10; x >= y // false y >= x // true z >= x // true
<=
Less than Equal To Operator (<=) checks whether the value of the left operand is less than or equal to the right operand, and if the statement is true, the operator is said to be the Less than Equal To Operator. The less than or equal to operator <= returns true - if the left operand is either less than or equal to the right false - if the left operand is greater than right int x = 10; int y = 15; x > y // false y > x // true
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/* Relational Operators are used for the comparison of the values of two operands. For example, checking if one operand is equal to the other operand or not, an operand is greater than the other operand or not, etc. Some of the relational operators are (==, >= , <= ). */ #include <iostream> using namespace std; main() { int a = 21; int b = 10; int c ; if( a == b ) { cout << "Line 1 - a is equal to b" << endl ; } else { cout << "Line 1 - a is not equal to b" << endl ; } if( a < b ) { cout << "Line 2 - a is less than b" << endl ; } else { cout << "Line 2 - a is not less than b" << endl ; } if( a > b ) { cout << "Line 3 - a is greater than b" << endl ; } else { cout << "Line 3 - a is not greater than b" << endl ; } /* Let's change the values of a and b */ a = 5; b = 20; if( a <= b ) { cout << "Line 4 - a is either less than \ or equal to b" << endl ; } if( b >= a ) { cout << "Line 5 - b is either greater than \ or equal to b" << endl ; } return 0; }


This represents the queue dequeue function. Every time another object or customer enters the line to wait, they join the "end of the line" and represent the "enqueue function". Queue
Control statement itself has three parts: for ( "initialization"; test condition; run every time command ). "Initialization" part is performed only once at for loop start. We can initialize a
Example to print all 'prime numbers' between two numbers in C++ Language. This problem is solved using nested for loop and if...else. In this program, the while loop is iterated times.