APECET/TSECET 2026 CSE – Day 1 Morning Blog

Topic: Structure of a C Program + Keywords & Identifiers

Welcome to Day 1 of your APECET & TSECET 2026 CSE preparation!
We’re starting with the foundation of C programming — the structure of every C program, and the essential building blocks: keywords and identifiers.

This blog includes:

✅ Easy concept notes
✅ 10 most expected MCQs
✅ Detailed answer key and explanations
✅ SEO-optimized layout + Telegram PDF prompt

Concept Notes: Structure of a C Program + Keywords & Identifiers

🔹 1. Structure of a C Program

A basic C program is written using the following parts:

#include <stdio.h>    // Preprocessor Directive

int main() {          // Main Function
    printf("Hello");  // Statements go here
    return 0;         // Exit status
}

#include <stdio.h>    // Preprocessor Directive

int main() {          // Main Function
    printf("Hello");  // Statements go here
    return 0;         // Exit status
}

Explanation of Each Part:

• #include <stdio.h> – Adds standard input/output functions like printf(), scanf() to your program.
• int main() – Every C program starts executing from this main function.
• { ... } – Group the body of the function.
• return 0; – Indicates that the program completed successfully.

🔹 2. Keywords in C

• Keywords are reserved words that have special meaning in C.
• You cannot use them for variable or function names.

Examples:

int, float, return, if, else, for, while, void, break

int, float, return, if, else, for, while, void, break

These are fixed and predefined. You cannot use:

int int = 5;  // ❌ Invalid – 'int' is a keyword

int int = 5;  // ❌ Invalid – 'int' is a keyword

3. Identifiers in C

• Identifiers are custom names given to variables, functions, arrays, etc.
• They must follow specific rules:

✅ Rules for Identifiers:

🧠 10 MCQs – Day 1 Practice Set

❗ Attempt these before checking answers below.

1️⃣ Which part of the C program is executed first?
A) #include
B) main()
C) return 0
D) printf()

2️⃣ Which of the following is a valid C identifier?
A) int
B) 2value
C) my_value
D) return

3️⃣ What is the purpose of #include <stdio.h> in C?
A) To begin the program
B) To allow printing & input functions
C) To create variables
D) To define main()

4️⃣ How many keywords are there in C (C89 standard)?
A) 16
B) 32
C) 64
D) 128

5️⃣ Which one is not a keyword in C?
A) return
B) void
C) class
D) for

6️⃣ What symbol is used to end a statement in C?
A) .
B) :
C) ;
D) ,

7️⃣ What will happen if main() is missing in a C program?
A) Error: No output
B) Code runs normally
C) It creates a warning
D) It automatically adds it

8️⃣ Which of these is an invalid identifier?
A) _temp
B) while
C) data2
D) sum

9️⃣ What does return 0; mean in C?
A) Print 0
B) Exit program with success
C) Loop ends
D) Nothing happens

🔟 Why can’t we use keywords as variable names?
A) Compiler crashes
B) They are reserved for specific meanings
C) They’re not supported by compilers
D) They’re too short

✅ Answer Key

🧠 Explanations for MCQs

• Q1: main() is the entry point where execution starts.
• Q2: my_value is a valid name; int and return are keywords; 2value starts with digit — invalid.
• Q3: #include <stdio.h> allows use of functions like printf() and scanf().
• Q4: C has 32 keywords in C89 standard.
• Q5: class is a C++ keyword, not part of C.
• Q6: In C, every statement must end with a semicolon (;).
• Q7: Missing main() = compile error. The program won’t run.
• Q8: while is a keyword and cannot be used as an identifier.
• Q9: return 0; tells OS that program ran without errors.
• Q10: Keywords are reserved by compiler, so cannot be re-used for naming.

📥 Download Today’s Notes + MCQ PDF

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💬 Comment Task for Learners

🗣️ Which part of today’s topic was confusing – return 0, main(), or identifier rules?
Drop your doubt in comments. We’ll pick it for explanation in our next YouTube Shorts!