What a program is

ACompressed recap

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A program is a list of instructions. You write source code in C; the compiler checks it and translates it into an executable of machine code. Every program starts inside main, runs its statements top to bottom (each ends with ;), and finishes with return 0;. printf prints exactly the characters of its string literal; escape sequences such as \n are single characters; comments vanish, except inside quotes.

Memory is a row of one-byte boxes numbered by address. A variable is a named box (an int takes 4 bytes here). = evaluates the right side with current values and overwrites the box. %d prints a whole-number value.

BMerged rule card

0.1.1 Programs and instructions; source code → compiler → executable; the shape of a first C program (main, printf, return)

• Program = list of instructions; processor runs machine code (0s and 1s).
• Source code (.c) → compiler → executable. Rule broken → compile-time error, nothing runs.
• Shape: #include <stdio.h> · int main(void) { … return 0; }.
• Statements run top to bottom; each ends with ;.
• printf("…") prints exactly the string literal; it never adds a new line.
• Escapes (one character each): \n new line, \t tab, \\ backslash, \" quote.
• Comments: /* … */ (not nestable) and // …; inside quotes they are plain text.

0.1.2 Memory as numbered boxes: bits, bytes, addresses; a variable as a named box

• bit = 0 or 1; byte = 8 bits; n bits → patterns double with each bit (8 bits → 256).
• Memory = numbered one-byte boxes; number = address; multi-byte value’s address = its first byte.
• int = whole number, 4 bytes here; int x = 5; creates and fills a box.
• x = expr; evaluate right side with current values, then overwrite x.
• Unfilled local variable = unpredictable value.
• %d in printf = placeholder for the next value, as a whole number.
• Identifier: letters, digits, _; not starting with a digit; not a keyword; case-sensitive.
• Swap needs a third variable: t = a; a = b; b = t;

CInterleaved GATE-style questions

Q1MCQ1 markOutput

What does this print?

printf("1\t2\n3");
printf("4\n");

• (A) 1 2 3 4 on one line
• (B) 12 on line 1; 34 on line 2
• (C) 1, tab, 2, 3 on line 1; 4 on line 2
• (D) 1, tab, 2 on line 1; 34 on line 2

Q2NAT1 markEscape sequences

How many characters are printed by printf("\\n\n");?

Numerical answer: ________

Q3MCQ1 markCompiler

Which problem stops the program from being built into an executable?

• (A) Printing the same text twice
• (B) Writing Printf instead of printf
• (C) Forgetting \n at the end of a printf
• (D) A comment containing the word main

Q4MCQ2 marksOutput

What does this print?

int a = 7;
int b = 2;
a = a + b;
b = a - b;
a = a - b;
printf("%d %d\n", a, b);

• (A) 7 2
• (B) 2 7
• (C) 9 7
• (D) 2 2

Q5NAT1 markAddresses

Three ints are stored one after another starting at address 500 (4 bytes each). What is the address of the third int?

Numerical answer: ________

Q6MSQ1 markVariables

Which statements are true?

• (A) = in C asks whether two values are equal.
• (B) A variable created without a first value may hold any value.
• (C) x = x + 1; is valid C and increases x by 1.
• (D) The name Total refers to the same variable as total.

Q7NAT1 markBits

How many different patterns can one byte hold?

Numerical answer: ________

Q8MCQ1 markComments

How many times is the word OK printed?

printf("OK\n"); /* printf("OK\n");
printf("OK\n"); */ printf("OK\n");
// printf("OK\n");

• (A) 4
• (B) 1
• (C) 2
• (D) 3

Q9MCQ2 marksOutput

What does this print?

int k = 4;
printf("%d", k);
k = k + k;
printf("%d\n", k + 1);

• (A) 49
• (B) 4 then 9 on the next line
• (C) 48
• (D) 4 9

DAnswer Vault