Introduction to C Language: Syntax, Variables, Control Flow & Functions

C might be one of the most foundational languages for any computer science career. It forms the core syntax of modern languages like C++, Java, C#, and JavaScript, and remains essential for operating systems, embedded hardware, and high-performance computing.

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1. Creating Your First Program

All executable code in C lives inside functions. The operating system starts execution at a mandatory, deterministic function: main().

#include <stdio.h>

int main() {
    printf("Hello World\n");
    return 0;
}

• #include <stdio.h> imports the Standard Input/Output header file.
• printf() outputs text to the standard terminal.
• return 0; signals successful execution to the host OS.

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2. Variables & Primitive Data Types

In C, variables must be explicitly typed before use:

int age = 25;
float height = 1.78;
char grade = 'A';
char name[] = "Morad";

Placeholders for printf()

• %d or %i: Integers
• %f: Floating point numbers
• %c: Characters
• %s: Strings (character arrays)

printf("Name: %s, Age: %d, Height: %.2fm\n", name, age, height);

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3. Reading Input with scanf()

To read user input from the keyboard, use scanf() with the memory address operator &:

#include <stdio.h>

int main() {
    int age;
    printf("Enter your age: ");
    scanf("%d", &age);
    printf("You entered: %d\n", age);
    return 0;
}

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4. Control Flow: Conditions & Loops

Conditionals (if, else, switch)

if (age >= 18) {
    printf("Adult\n");
} else {
    printf("Minor\n");
}

Switch Statements

switch (day) {
    case 1: printf("Monday\n"); break;
    case 2: printf("Tuesday\n"); break;
    default: printf("Other day\n"); break;
}

Loops (for, while, do-while)

// For loop
for (int i = 0; i < 5; i++) {
    printf("Iteration %d\n", i);
}

// While loop
int count = 0;
while (count < 3) {
    printf("Count: %d\n", count);
    count++;
}

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5. Functions

Functions keep code modular and readable:

#include <stdio.h>

int square(int num) {
    return num * num;
}

int main() {
    int val = 5;
    printf("Square of %d is %d\n", val, square(val));
    return 0;
}

Practicing writing small programs is the key to mastering C language syntax!