Most examples you see of C++ use the so-called stream output for the code. Stream output uses the << operator, as shown in this example:
However, C++ inherits another form of output from its predecessor, C. This form is based upon a set of functions that are very similar both in appearance and in the way they function. Collectively these functions carry the name of their most widely used member, printf().
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You can ignore this article and continue using stream output, or you can switch over to printf() output if you prefer — but you should not mix the two in the same program. These sets of functions use different classes for buffering output to reduce the number of disk accesses, thereby increasing program performance. Mixing the two will cause output to get interleaved in unpredictable ways resulting in confusing and perhaps meaningless output.
The printf() function has the following prototype defined in the cstdio include file:
The ellipses (…) in a prototype declaration means any number of any type of variables.
The first argument to printf() is a string to be output. If this string contains format specifiers, which are characters preceded by a ‘%’, then printf() outputs the next argument in line using that format specifier as guidance.
This is best demonstrated with a simple example:
This would output the string
There must be at least as many arguments following the format string as there are format specifiers in the string. If there are more, they are ignored. printf() returns the number of characters printed. If an error occurs, this number will be negative.
Format specifiers have the form
Each of these format specifiers is described in the following sections.
The following type specifiers are available to printf()
Type Specifier | Type | Example |
---|---|---|
d or i | Signed decimal integer | –123 |
u | Unsigned decimal integer | 456 |
o | Unsigned octal | 05670 |
x | Unsigned hexadecimal (lowercase) | 89abc |
X | Unsigned hexadecimal (uppercase) | 89ABC |
f, F | Decimal floating point | 123.456 |
e | Scientific notation (lowercase) | 1.23456e+2 |
E | Scientific notation (uppercase) | 1.23456E+2 |
g | The shorter of f or e | |
G | The shorter of F or E | |
a | Hexadecimal floating point (lowercase) | |
A | Hexadecimal floating point (uppercase) | |
c | Character | c |
s | char* (ASCIIZ string) | example |
p | Pointer address | bc080 |
% | The % character | % |
There is at least one type specifier for each of the variable types intrinsic to C++. In the absence of any further information, C++ uses default values. For example, an integer number output with a d is preceded with a – if it is negative but not preceded with anything if it is positive. In addition, such a value takes only as many spaces as are needed to output the number.
What if the default display format for an integer specifier such as d is not what you want? For example, for some applications, it might be important that positive numbers are preceded by a + (plus sign) in the same way that negatives are preceded by a – (minus sign). For that, printf() provides these output amplifier flags.
Flag | Operating on Type | Has the Following Effect |
---|---|---|
– | all | Left justify output. |
+ | numeric | Precedes positive numbers with a +. Negative numbers are always preceded by a -. |
space | numeric | Insert a blank if no sign is going to be written. |
# | o, x, or X | Precede number with 0, 0x,or 0X. |
# | a, A, e, E, f, F, g, G | Include a decimal point even if the fractional part of the number is zero. |
0 | number | Left-pad the number with zeroes (useful when printing dollar amounts). |
Suppose that you want all of the numbers in a column to line up. In that case, it would be important that each number occupy the same number of spaces even if not all of those spaces are needed to display the value. For this and thousands of other applications, printf() allows the user to specify the width by using these width flags.
Width | Meaning |
---|---|
number | The minimum number of characters to allocate for this field. |
* | The width is specified in an integer argument to printf() preceding the number to be formatted. |
The precision flag is most often combined with the width flag when displaying floating point numbers. In this case, the precision flag tells printf() how many digits to display after the decimal point.
The precision flag has been given meaning for types other than floating point, as shown here, but these are less commonly used.
Precision | Operating on type | Has the following effect |
---|---|---|
number | d, i, o, u, x, X (integer types) | The minimum number of characters to output. Pad on the left with 0’s if necessary. |
number | a, A, e, E, f, F (floating point types) | The number of digits to print after the decimal point. |
number | g, G (floating point types) | The maximum number of significant digits to be printed. |
number | s (character string) | The maximum number of characters to output. |
blank | all | A period not followed by a number is the same as a precision of 0. |
* | all | The precision is specified in an integer argument to printf() preceding the number to be formatted. |
Unlike the flags discussed above, the length flag is not so much about telling printf() how to display the number but more about telling printf() about the number itself. For example, suppose you want to output a variable using a d format, but that variable is actually a long int? No problem, just use ld,as described here.
Length | d, i | u, o, x, X | decimal | c | s |
---|---|---|---|---|---|
none | in | unsigned int | double | int | char* |
hh | signed char | unsigned char | |||
h | signed short | unsigned short | |||
l | long | unsigned long | wchar_t | wchar_t* | |
ll | long long | unsigned long long | |||
L | long double |
The printf() style of output has one significant advantage compared with stream output: the grammar is extremely terse. Once you’ve master all the special types and lengths, widths and precisions, you can output a variable in just about any way you want with a minimum number of keystrokes.
The terseness comes with a price, however:
The terseness makes printf() output difficult for the uninitiated to understand.
printf() is not type safe.
If you say to output the next field using a %Lf, then printf() will assume that a long double is waiting there. It has no way to double check. If a simple double or (heaven forbid!) an integer is the next variable on the stack, then printf() Precision tune auto care online garage. will output garbage. Worse yet, it will continue to output garbage from that point forward since now the specifiers and the arguments are out of sync.
printf() is not extensible.
The writers of printf() thought of a lot of different types of variables, but if they didn’t think of it, then you’re out of luck.
C programs with output showing usage of operators, loops, functions, arrays, performing operations on strings, files, pointers. Download executable files and execute them without compiling the source file. Code::Blocks IDE is used to write programs, most of these will work with GCC and Dev C++ compilers. The first program, prints 'Hello World.'
Example 1 - C hello world program
/** My first C program */
Output of program:
'Hello World'
Example 2 - C program to get input from a user using scanf
#include <stdio.h>int main()
{
int x;
printf('Input an integern');
scanf('%d',&x);// %d is used for an integer
printf('The integer is: %dn', x);
return0;
}
Output:
Input an integer
7897
The integer is: 7897
Example 3 - using if else control instructions
#include <stdio.h>int main()
{
int n;
printf('Enter a numbern');
scanf('%d',&n);
if(n >0)
printf('Greater than zero.n');
else
printf('Less than or equal to zero.n');
return0;
}
Output:
Enter a number
-45
Less than or equal to zero.
Example 4 - while loop example
Output:
1 2 3 4 5 6 7 8 9 10
Example 5 - C program check if an integer is prime or not
Example 6 - command line arguments
#include <stdio.h>int main(int argc,char*argv[])
{
int c;
printf('Number of command line arguments passed: %dn', argc);
for(c =0; c < argc; c++)
printf('%d argument is %sn', c +1, argv[c]);
return0;
}
This program prints the number of arguments and their contents.
Example 7 - Array program
#include <stdio.h>int main()
{
int array[100], n, c;
printf('Enter number of elements in arrayn');
scanf('%d',&n);
printf('Enter %d elementsn', n);
for(c =0; c < n; c++)
scanf('%d',&array[c]);
printf('The array elements are:n');
for(c =0; c < n; c++)
printf('%dn', array[c]);
return0;
}
Example 8 - function program
#include <stdio.h>void my_function();// Declaring a function
int main()
{
printf('Main function.n');
my_function();// Calling the function
printf('Back in function main.n');
return0;
}
// Defining the function
void my_function()
{
printf('Welcome to my function. Feel at home.n');
}
Example 9 - Using comments in a program
Example 10 - using structures in C programming
#include <stdio.h>struct game
{
char game_name[50];
int number_of_players;
};// Note the semicolon
int main()
{
struct game g;
strcpy(g.game_name,'Cricket');
g.number_of_players=11;
printf('Name of game: %sn', g.game_name);
printf('Number of players: %dn', g.number_of_players);
return0;
}
Example 11 - C program for Fibonacci series
#include <stdio.h>int main()
{
int n, first =0, second =1, next, c;
printf('Enter the number of termsn');
scanf('%d',&n);
printf('First %d terms of Fibonacci series are:n', n);
for(c =0; c < n; c++)
{
if(c <=1)
next = c;
else
{
next = first + second;
first = second;
second = next;
}
printf('%dn', next);
}
return0;
}
Example 12 - C graphics programming
#include <graphics.h>int main()
{
int gd = DETECT, gm;
initgraph(&gd,&gm,'C:TCBGI');
outtextxy(10,20,'Graphics programming is fun!');
circle(200,200,50);
setcolor(BLUE);
line(350,250,450,50);
getch();
closegraph();
return0;
}
If you are using GCC on Linux operating system, then you may need to modify the programs. For example, consider the following program that prints the first ten natural numbers.
#include <stdio.h>int main()
{
int c;
for(c =1; c <=10; c++)
printf('%dn', c);
getch();
return0;
}
The program includes a header file <conio.h>
and uses function getch, but this file is Borland specific, so it works in Turbo C compiler but not in GCC. The program for GCC must be like:
int main()
{
int c;
/* for loop */
for(c =1; c <=10; c++)
printf('%dn', c);
return0;
}
If you are using GCC, save the program in a file say 'numbers.c' to compile the program, open the terminal and enter the command 'gcc numbers.c', this compile the program and to execute it enter the command './a.out' do not use quotes while executing commands. You can specify the output file name as 'gcc numbers.c -o numbers.out', to run execute './numbers.out' in the terminal.
A program consists of functions that contain instructions given to a machine to perform a task. The process of writing it includes designing an algorithm, drawing a flowchart, and then writing code. After writing it, you need to test it and debug it if it does not produce the required output.
To write a program, you need a text editor (use your favorite one) and a compiler. A compiler converts source code into machine code, which consists of zero's and one's only, ready to be executed on a machine.
An IDE (Integrated Development Environment) provides a text editor, compiler, debugger, etc. for developing programs and managing projects. Code::Blocks IDE provides an ideal environment for development. It can import Microsoft Visual C++ projects, is extendable as it uses plug-ins, open-source, and cross-platform.
A program must have at least one function which must be main. A function consists of declarations and statements. A statement is an expression followed by a semicolon. For example, a + b, printf('C program examples') are expressions and a + b; and printf('C is an easy to learn computer programming language'); are statements.
To use a variable, we must indicate its type, whether it is an integer, float, character, or others. C language has many built-in data types, and we can create our own using structures and unions. Every data type has its size that may depend on the machine; for example, an integer may be of 2 or 4 Bytes. Data is stored in a binary form, i.e., a group of bits where each bit can be '0' or '1'.
Keywords such as 'switch,' 'case,' 'default,' 'register,' are reserved words with predefined meaning and can't be used as the name of a variable or a function. Memory can be allocated at compile-time or run-time using malloc and calloc functions. C language has many features such as recursion, preprocessor, conditional compilation, portability, pointers, multi-threading by using external libraries, dynamic memory allocation. Thanks to these, it is used for making portable software programs and applications. Using networking API's users can communicate and interact with each other and share files.
C standard library contains functions for mathematical operations, characters, input/output, files, and many more. The process of making a program which is known as coding requires knowledge of programming language and logic to achieve the desired output. So you should learn C programming basics and start making programs.
Learning data structures (stacks, queues, linked lists) using C provides you a greater understanding as you learn everything in detail. A general belief is to go for high-level languages. However, it's a good idea to learn C before learning C++ or Java. C++ is object-oriented and contains all features of C, so learning C help you learn C++ quickly, then you can study Java.
If you are a beginner, buy any one of the first two books, and if you have previous programming experience or you know the basics of C language, buy the third one.