{"id":58633,"date":"2019-06-10T12:01:23","date_gmt":"2019-06-10T06:31:23","guid":{"rendered":"https:\/\/data-flair.training\/blogs\/?p=58633"},"modified":"2021-06-10T13:57:31","modified_gmt":"2021-06-10T08:27:31","slug":"constants-in-c-and-c-plus-plus","status":"publish","type":"post","link":"https:\/\/data-flair.training\/blogs\/constants-in-c-and-c-plus-plus\/","title":{"rendered":"5 Types of Constants in C and C++ and How they’re Different from Literals"},"content":{"rendered":"

Have you ever thought, what are constants and why they are an important part of the programming world? We have got all the answers to your queries.\u00a0Constants in C and C++ programming are nothing but fixed values that cannot be altered throughout the program run. These fixed values are also called as literals<\/strong><\/em>.<\/p>\n

In layman language, we can use the terms constants and literals interchangeably<\/em>. But, we will highlight the key difference between the two in this tutorial.<\/p>\n

Before we start, you must be aware of the\u00a0Variables in C<\/a>\u00a0<\/strong><\/em><\/p>\n

Now, let us acknowledge the significance of constants and literals in C and C++ by considering the following problem:<\/p>\n

There are certain situations where variables do not change their value, let\u2019s say, the value of pi, approximately equal to 3.14159 is constant and it can never change which is a universal fact.\u00a0We might encounter several situations, where we would require pi for mathematical calculations. Similarly, we can assign constant values to several variables according to our convenience.<\/p>\n

1. Variables and Constants in C and C++<\/h2>\n

It is important to note that a variable connotes a different meaning in programming and mathematics. A variable is nothing but a value that we can store in computer memory.<\/em> We can easily change its value during run-time.<\/span> In contrast to that, constants never change their value throughout the program run. Constants can hold any of the data types available in C and C++<\/a><\/strong><\/em>.<\/p>\n

2. Declare or Define Constants<\/h2>\n

We can assign C\/C++ constant value to a variable in two ways:<\/p>\n

    \n
  1. Using #define, a preprocessor directive:<\/strong> We have already discussed #define in detail in preprocessors.<\/li>\n
  2. Using the keyword const:<\/strong> It is similar to variable declaration except that we should add the keyword \u201cconst\u201d prior to it. It is important to assign a value to the constant as soon as we declare it.<\/li>\n<\/ol>\n

    2.1 Declare or Define Constants in C<\/h4>\n

    Here is a program in C that illustrates what happens when we try to modify the value of a constant:<\/p>\n

    #include<stdio.h>\r\nint main()\r\n{\r\n\r\nprintf(\"Welcome to DataFlair tutorials!\\n\\n\");\r\n\r\nconst float pi = 3.14;\r\nconst float e = 2.71;\r\n\r\npi = 3.14159;\r\nprintf(\"The value of pi is: %f\", pi);\r\nreturn 0;\r\n}<\/pre>\n
    Output-<\/b><\/p>\n
    \"modify<\/a><\/p>\n
    2.1 Declare or Define Constants in C++<\/h4>\n
    The same issue arises when we try to modify the value of a constant:<\/p>\n
    #include <iostream>\r\nusing namespace std;\r\n\r\nint main()\r\n{\r\n\r\ncout<<\"Welcome to DataFlair tutorials!\"<<endl<<endl;\r\n\r\nconst float pi = 3.14;\r\nconst float e = 2.71;\r\n\r\npi = 3.14159;\r\ncout<<\"The value of pi is: \"<< pi <<endl;\r\nreturn 0;\r\n}\r\n<\/pre>\n
    Error-<\/strong><\/p>\n
    \"Declare<\/a><\/p>\n
    3. Constants vs Literals in C\/C++<\/h2>\n
    As discussed earlier, constants and literals may be used interchangeably but there is a slight difference between the two.<\/p>\n
    Let us consider a simple example to better understand it.<\/p>\n
    In India, the legal voting age is 18.<\/p>\n
    Therefore, we define,<\/p>\n
    const voting_age = 18;<\/em><\/strong><\/p>\n
    Here, 18 is a literal, a value that is expressed as itself whereas a constant can be considered a data type that is substituted in place of a literal to enhance the functionality of the code.<\/p>\n
    Now, we wish to print the message, \u201c You are allowed to vote! \u201d for people of age greater than or equal to 18.<\/p>\n
    Here is a segment of code in C in accordance with the statement above.<\/strong><\/p>\n
    if (age >= voting_age)<\/em>
    \n{<\/em>
    \nprintf(\u201c You are allowed to vote! \u201d);<\/em>
    \n}<\/em><\/p>\n
    Here, the identifier voting_age<\/strong> is constant.<\/p>\n
    Here is a segment of code in C++ in accordance with the statement above.<\/strong><\/p>\n
    if (age >= voting_age)<\/em>
    \n{<\/em>
    \ncout<<\u201c You are allowed to vote! \u201d<<endl;<\/em>
    \n}<\/em><\/p>\n
    Here, the identifier voting_age is constant.<\/p>\n
    4. Types of Constants in C and C++<\/h2>\n
    In the C\/C++, there are 5 different types of constants depending upon their Data type:<\/em><\/p>\n
    \"Types<\/a><\/p>\n
    4.1 Integer Constants<\/h3>\n
    \n
    \n
    As the name itself suggests, an integer constant is an integer with a fixed value, that is, it cannot have fractional value like 10, -8, 2019.<\/span><\/div>\n<\/div>\n<\/div>\n
    For example,<\/p>\n
    const signed int limit = 20;<\/strong><\/p>\n
    We may use different combinations of U and L suffixes to denote unsigned and long modifiers respectively, keeping in mind that its repetition does not occur.<\/p>\n
    We can further classify it into three types, namely:<\/p>\n