Basic Structure of a C Program
A C program is made of declarations, functions and statements. For a small program, the most important pieces are the header include, the main() function, executable statements and the return value.
Minimal C Program Top ↑
#include <stdio.h>
int main(void) {
printf("Hello, World!\n");
return 0;
}Output
Hello, World!- C is case-sensitive:
printfandPrintfare different names. - Most simple statements end with a semicolon.
- Variables must be declared before they are used.
- Braces
{ }group the body of a function or control statement. - Execution of a normal program begins in
main().
What Each Part Does Top ↑
#include <stdio.h> supplies declarations for standard input/output functions such as printf() and scanf(). The main() function is the program entry point. The final return 0; indicates successful completion.
Comments in a C Program Top ↑
// A single-line comment
/* A block comment
can continue on another line. */Comments are ignored by the compiler as program instructions. See the C comments tutorial for more examples.
Read a Name and Display It Top ↑
The full page structure is already shown above, so this example focuses on the changed declarations and input/output statements.
char name[30];
printf("Enter your name: ");
scanf("%29s", name);
printf("Welcome %s\n", name);Key change: %29s limits the number of characters written into the 30-character array. scanf("%s", ...) reads a word and stops at whitespace.
Sum of Two Integers Top ↑
int a = 4;
int b = 5;
int sum = a + b;
printf("Sum = %d\n", sum);Output
Sum = 9Sum and Average of Three Numbers Top ↑
int a = 3;
int b = 5;
int c = 6;
int sum = a + b + c;
double average = sum / 3.0;
printf("Sum = %d\n", sum);
printf("Average = %.2f\n", average);Output
Sum = 14
Average = 4.67Key change: dividing by 3.0 performs floating-point division.
Command-Line Arguments Top ↑
#include <stdio.h>
int main(int argc, char *argv[]) {
if (argc > 1) {
printf("Argument received: %s\n", argv[1]);
} else {
printf("No argument received.\n");
}
return 0;
}Preprocessor Constant Top ↑
#include <stdio.h>
#define PI 3.14
int main(void) {
printf("The value of PI: %.2f\n", PI);
return 0;
}Preserved Example: Sum and Average from User Input Top ↑
The original page also had a second sum-and-average program where all three values are entered by the user. That variation is preserved here separately.
#include <stdio.h>
int main(void) {
int a, b, c;
printf("Enter three integers: ");
if (scanf("%d %d %d", &a, &b, &c) != 3) {
printf("Invalid input.\n");
return 1;
}
int sum = a + b + c;
double average = sum / 3.0;
printf("Sum = %d\n", sum);
printf("Average = %.2f\n", average);
return 0;
}Related C Programming Examples
Subhendu Mohapatra
Author & Instructor at plus2net
I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.
