C++ Programming Code Examples
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Count letters.
/* Count letters. */
#include <iostream>
#include <fstream>
#include <cctype>
using namespace std;
int alpha[26];
int main(int argc, char *argv[])
{
char ch;
if(argc!=2) {
cout << "Usage: COUNT <source>\n";
return 1;
}
ifstream in(argv[1]);
if(!in) {
cout << "Cannot open input file.\n";
return 1;
}
// init alpha[]
int i;
for(i = 0; i <26; i++) alpha[ i ] = 0;
while(!in.eof()) {
ch = in.get();
if(isalpha(ch)) {
ch = toupper(ch);
alpha[ch-'A']++;
}
};
for(i = 0; i <26; i++) {
cout << (char) ('A'+ i) << ": " << alpha[ i ] << '\n';
}
in.close();
return 0;
}
In computer programming, loops are used to repeat a block of code. For example, when you are displaying number from 1 to 100 you may want set the value of a variable to 1 and display it 100 times, increasing its value by 1 on each loop iteration. When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop. A for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times.
Convert lowercase letter to uppercase. The toupper() function in C++ converts a given character to uppercase. It is defined in the cctype header file. Converts c to its uppercase equivalent if c is a lowercase letter and has an uppercase equivalent. If no such conversion is possible, the value returned is c unchanged. Notice that what is considered a letter may depend on the locale being used; In the default "C" locale, a lowercase letter is any of: a b c d e f g h i j k l m n o p q r s t u v w x y z, which translate respectively to: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z. The toupper() function takes the following parameter: c - a character, casted to int type or EOF. Function returns the uppercase equivalent to c, if such value exists, or c (unchanged) otherwise. The value is returned as an int value that can be implicitly casted to char.
Get characters. Extracts characters from the stream, as unformatted input. The get() function is used to read a character(at a time) from a file. The classes istream and ostream define two member functions get(), put() respectively to handle the single character input/output operations. There are two types of get() functions. Both get(char *) and get(void) prototype can be used to fetch a character including the blank space,tab and newline character. The get(char *) version assigns the input character to its argument and the get(void) version returns the input character. Since these functions are members of input/output Stream classes, these must be invoked using appropriate objects.
Checks whether c is an alphabetic letter. Notice that what is considered a letter depends on the locale being used; In the default "C" locale, what constitutes a letter is only what returns true by either isupper or islower. Using other locales, an alphabetic character is a character for which isupper or islower would return true, or another character explicitly considered alphabetic by the locale (in this case, the character cannot be iscntrl, isdigit, ispunct or isspace). For a detailed chart on what the different ctype functions return for each character of the standard ANSII character set, see the reference for the <cctype> header. In C++, a locale-specific template version of this function (isalpha) exists in header <locale>.
In while loop, condition is evaluated first and if it returns true then the statements inside while loop execute, this happens repeatedly until the condition returns false. When condition returns false, the control comes out of loop and jumps to the next statement in the program after while loop. The important point to note when using while loop is that we need to use increment or decrement statement inside while loop so that the loop variable gets changed on each iteration, and at some point condition returns false. This way we can end the execution of while loop otherwise the loop would execute indefinitely. A while loop that never stops is said to be the infinite while loop, when we give the condition in such a way so that it never returns false, then the loops becomes infinite and repeats itself indefinitely.
Consider a situation, when we have two persons with the same name, jhon, in the same class. Whenever we need to differentiate them definitely we would have to use some additional information along with their name, like either the area, if they live in different area or their mother's or father's name, etc. Same situation can arise in your C++ applications. For example, you might be writing some code that has a function called xyz() and there is another library available which is also having same function xyz(). Now the compiler has no way of knowing which version of xyz() function you are referring to within your code.
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, 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.
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Check whether eofbit is set. Returns true if the eofbit error state flag is set for the stream. This flag is set by all standard input operations when the End-of-File is reached in the sequence associated with the stream. Note that the value returned by this function depends on the last operation performed on the stream (and not on the next). Operations that attempt to read at the End-of-File fail, and thus both the eofbit and the failbit end up set. This function can be used to check whether the failure is due to reaching the End-of-File or to some other reason.
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.
#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.
Lets see a sample without break statement, then we will discuss switch case with break 'Switch Case' statement is mostly used with 'break statement' even though the break is
