Structured Programming

1) Print Hello Word 
Let us look at a simple code that would print the words "Hello World": 
#include <stdio.h> 
int main() 
{ 
/* my first program in C */ 
printf("Hello, World! \n"); 
return 0; 
} 
Let us look various parts of the above program: 
1. The first line of the program #include <stdio.h> is a preprocessor command, which tells 
a C compiler to include stdio.h file before going to actual compilation. 
2. The next line int main() is the main function where program execution begins. 
3. The next line /*...*/ will be ignored by the compiler and it has been put to add additional 
comments in the program. So such lines are called comments in the program. 
4. The next line printf(...) is another function available in C which causes the message 
"Hello, World!" to be displayed on the screen. 
5. The next line return 0; terminates main()function and returns the value 0. 
Note: Compile & Execute C Program: 
Let‘s look at how to save the source code in a file, and how to compile and run it. Following are 
the simple steps: 
1. Open a text editor and add the above-mentioned code. 
2. Save the file as hello.c 
3. Open a command prompt and go to the directory where you saved the file. 
4. Type gcc hello.c and press enter to compile your code.  
5. If there are no errors in your code the command prompt will take you to the next line and 
would generate a.out executable file. 
6. Now, type a.out to execute your program. 
7. You will be able to see "Hello World" printed on the screen 
2) Declaring Variable Inputing and Outputting Value 
A variable is nothing but a name given to a storage area that our programs can manipulate.  
Each variable in C has a specific type, which determines the size and layout of the variable's 
memory; the range of values that can be stored within that memory; and the set of operations 
that can be applied to the variable. 
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a) Working with variables - Let's look at an example of how to declare an integer variable in 
the C language, assign value and read the value in the variable to output. 
For example: 
int age; 
In this example, the variable named age would be defined as an int. 
Below is an example C program where we declare this variable: 
#include <stdio.h> 
int main() 
{ 
int age; 
age = 10; 
printf("TechOnTheNet.com is over %d years old.\n", age); 
return 0; 
} 
This C program would print "TechOnTheNet.com is over 10 years old." 
Conversion specifiers are made up of two characters: % and a special character. 
The special character tells the program how to convert the data. 
Conversion Specifier Description 
%d 
%f 
%c 
Displays integer value 
Displays floating-point numbers 
Displays character 
Format specifiers are the operators used in printf() function to print the data which is referred by an 
object or a variable. when a value is stored in a particular variable, Then we cannot print the value 
stored in the variable directly with out the using format specifiers. We can retrieve the data stored in 
the variables and can print them on to the console screen by using these format specifiers in a printf 
function. Format specifiers start with a percentage(%) symbol and follows a special character to identify 
the type of the data. There are basically six types of format specifiers are available in c they are  
%d - represent integer values 
%f - represent  float values 
%c - represent single character values 
%s - represent  string values 
%u - represent the address of a variable  
%ld – represent Long  integer values 
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More examples: Use the printf function with formatting options. 
#include <stdio.h> 
main(){ 
int x; 
float y; 
char c; 
x = -4443; 
y = 554.21; 
c = 'M'; 
printf("\nThe value of integer variable x is %d", x); 
printf("\nThe value of float variable y is %f", y); 
printf("\nThe value of character variable c is %c\n", c); 
} 
The value of integer variable x is -4443 
The value of float variable y is 554.210022 
The value of character variable c is M 
More examples: Use the scanf function with formatting options assign to assign value to 
variables. 
This C program would print "Your Name is Kim and you age  is over 10 yrs old." 
#include <stdio.h> 
main(){ 
int Age; 
char Name[10]; 
printf("\nPlz enter your Name "); 
scanf(“%s”,&Name); 
printf("\nPlz enter your Age", y); 
scanf(“%d”,&Age): 
printf("\nYour Name is %s and your age is %d yrs old\n",Name,Age); 
} 
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