1. Iterative Control Structures: for, while, and do-while

Iterative control structures (loops), mathematical series summation, and number theory algorithms form the backbone of Unit 2 in MAKAUT C Programming (PPS-II). In university end-semester papers, Unit 2 accounts for over 25 to 30 marks, including mandatory pattern-printing questions in Group B and multi-part numerical algorithms in Group C.

This comprehensive guide covers loops, jump statements, series evaluation formulas, and 40+ solved programs straight from unit_2_loops_series_number_patterns.

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1. Comparative Analysis of C Loops

A loop repeatedly executes a block of code until a specified test condition evaluates to false (0).

Feature`for` loop`while` loop`do-while` loop
Control TypeEntry-ControlledEntry-ControlledExit-Controlled
Minimum Executions0 times0 timesAt least 1 time
Best ForKnown number of iterationsCondition-driven iterationsMenu-driven interactive programs
Syntaxfor(init; cond; upd)while(cond)do { ... } while(cond);
NOTE

In do-while(condition);, the trailing semicolon is mandatory. Omitting it triggers a syntax error.

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2. Jump Statements: break, continue, goto

  • `break`: Exits the immediate loop or switch block unconditionally.
  • `continue`: Skips the remaining code in the current iteration and jumps directly to the loop update step.
  • `goto`: Performs an unconditional jump to a labeled statement (label:). Discouraged in modern software development as it breaks structured programming principles.

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3. Mathematical Series Summation Algorithms

In MAKAUT exams, series summation questions test your ability to translate mathematical summation formulas (\sum) into algorithmic accumulator variables (sum += term).

Series 1: \sum_{i=1}^{n} x^i = x + x^2 + x^3 + \dots + x^n

c
1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><math.h>
3 
4int main() {
5    int x, n;
6    double sum = 0.0;
7 
8    printf("Enter base(x) and limit(n): ");
9    scanf("%d %d", &x, &n);
10 
11    for (int i = 1; i <= n; i++) {
12        sum += pow(x, i);
13    }
14 
15    printf("Sum of series = %.2lf\n", sum);
16    return 0;
17}

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Series 2: Harmonic Fractional Series \sum_{i=1}^{n} 1i = 1 + 12 + 13 + \dots + 1n

c
1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2 
3int main() {
4    int n;
5    double sum = 0.0;
6 
7    printf("Enter n: ");
8    scanf("%d", &n);
9 
10    for (int i = 1; i <= n; i++) {
11        sum += 1.0 / i; // 1.0 ensures floating point division!
12    }
13 
14    printf("Harmonic Series Sum = %.4lf\n", sum);
15    return 0;
16}

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4. Solved Core Number Algorithms

1. Prime Number Check (Optimized O(\sqrt{n}) Time)

*Exam Context: Group B (5 Marks)*

c
1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdbool.h>
3 
4bool isPrime(int n) {
5    if (n <= 1) return false;
6    for (int i = 2; i * i <= n; i++) {
7        if (n % i == 0) return false;
8    }
9    return true;
10}
11 
12int main() {
13    int num;
14    printf("Enter number: ");
15    scanf("%d", &num);
16 
17    if (isPrime(num))
18        printf("%d is a Prime Number.\n", num);
19    else
20        printf("%d is NOT a Prime Number.\n", num);
21 
22    return 0;
23}

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2. Armstrong Number Check in a Given Range

An n-digit number is an Armstrong number if the sum of its digits raised to the n-th power equals the original number (e.g., 153 = 1^3 + 5^3 + 3^3).

c
1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><math.h>
3 
4int main() {
5    int low, high;
6    printf("Enter range(low high): ");
7    scanf("%d %d", &low, &high);
8 
9    printf("Armstrong numbers between %d and %d:\n", low, high);
10    for (int i = low; i <= high; i++) {
11        int temp = i, count = 0, sum = 0;
12 
13        // Step 1: Count number of digits
14        int t = i;
15        while (t > 0) { count++; t /= 10; }
16 
17        // Step 2: Sum digit powers
18        t = i;
19        while (t > 0) {
20            int rem = t % 10;
21            sum += (int)pow(rem, count);
22            t /= 10;
23        }
24 
25        if (sum == i) {
26            printf("%d ", i);
27        }
28    }
29    printf("\n");
30    return 0;
31}

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3. Krishnamurthy (Strong) Number Verification

A number is a Krishnamurthy number if the sum of the factorials of its digits equals the number itself (e.g., 145 = 1! + 4! + 5! = 1 + 24 + 120 = 145).

c
1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2 
3int factorial(int n) {
4    int fact = 1;
5    for (int i = 1; i <= n; i++) fact *= i;
6    return fact;
7}
8 
9int main() {
10    int num, temp, sum = 0;
11    printf("Enter integer: ");
12    scanf("%d", &num);
13 
14    temp = num;
15    while (temp > 0) {
16        int rem = temp % 10;
17        sum += factorial(rem);
18        temp /= 10;
19    }
20 
21    if (sum == num)
22        printf("%d is a Krishnamurthy Number.\n", num);
23    else
24        printf("%d is NOT a Krishnamurthy Number.\n", num);
25 
26    return 0;
27}

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4. Euclidean Algorithm for Greatest Common Divisor (GCD)

*Exam Context: Group B (5 Marks)*

c
1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2 
3int main() {
4    int a, b;
5    printf("Enter two numbers: ");
6    scanf("%d %d", &a, &b);
7 
8    int origA = a, origB = b;
9    while (b != 0) {
10        int temp = b;
11        b = a % b;
12        a = temp;
13    }
14 
15    printf("GCD of %d and %d = %d\n", origA, origB, a);
16    return 0;
17}

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5. Pattern Printing Mechanics

Pattern printing requires nested loop coordination:

  • Outer Loop (`i`): Controls row count.
  • Inner Loop 1: Prints leading space padding per row.
  • Inner Loop 2 (`j`): Prints characters/numbers per row.

Pyramid Star Pattern

c
1*
2   ***
3  *****
4 *******
5*********
c
1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2 
3int main() {
4    int rows;
5    printf("Enter number of rows: ");
6    scanf("%d", &rows);
7 
8    for (int i = 1; i <= rows; i++) {
9        // Outer loop controls rows
10        for (int space = 1; space <= rows - i; space++) {
11            printf(" ");
12        }
13        for (int j = 1; j <= (2 * i - 1); j++) {
14            printf("*");
15        }
16        printf("\n");
17    }
18    return 0;
19}

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6. MAKAUT Revision Summary

  • Always double check loop bounds (i < n vs i \le n) to avoid off-by-one errors.
  • For integer digit extractions, use rem = num % 10 followed by num /= 10.
  • In series problems, typecast division operands to float or double (1.0 / i) to prevent zeroing out integer division.