Here’s a simple example demonstrating the basic syntax and structure of a C program. This program takes two integers from the user, adds them, and displays the result:
#include <stdio.h> // Include standard input/output library int main() { // Main function: entry point of the program int num1, num2; // Declare two integer variables int sum; // Declare an integer to hold the result // Prompt the user to enter two integers printf("Enter first integer: "); scanf("%d", &num1); // Read first integer from user and store in num1 printf("Enter second integer: "); scanf("%d", &num2); // Read second integer from user and store in num2 sum = num1 + num2; // Add the two numbers and store the result in sum // Display the result printf("The sum of %d and %d is: %d\n", num1, num2, sum); return 0; // Return 0 to indicate successful execution }
Explanation of Code Structure and Syntax
1. Preprocessor Directive (#include <stdio.h>
)
#include <stdio.h>
is a preprocessor directive that includes the standard input/output library, which provides functions likeprintf
andscanf
for displaying text and receiving input from the user.- Directives starting with # are processed before compilation begins, allowing for library and macro inclusion.
2. Main Function (int main()
)
- The
main
function is the entry point for every C program. The execution of a program starts from this function. - It returns an integer value (
int
) to the operating system, which traditionally indicates success or failure.return 0
; at the end signals that the program ran successfully.
3. Variable Declarations
int num1, num2;
declares two integer variables,num1
andnum2
, which will hold the input values.int sum;
declares another integer variable,sum
, to store the result of the addition.
4. Input and Output
printf("Enter first integer: ");
prints a message prompting the user to input a value.scanf("%d", &num1);
reads an integer from user input and stores it innum1
. The%d
format specifier tellsscanf
to expect an integer, and&num1
is the address of the variable where the input is stored.- The same steps are repeated for
num2
.
5. Computation
- s
um = num1 + num2;
performs the addition ofnum1
andnum2
and stores the result in thesum
variable.
6. Displaying Results
printf("The sum of %d and %d is: %d\n", num1, num2, sum);
outputs the result.- The format specifier
%d
is used to insert the values ofnum1
,num2
, andsum
into the string, replacing each%d
with the corresponding value. \n
is a newline character, which moves the cursor to a new line after printing.
7. Return Statement
return 0
; ends the program, signaling that it finished successfully.