Add Day 6: More on loops

Author: sahilbansal17

Day 6/README.md

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+## More on Loops
+
+1. [Factorial of n using while loop](whileLoop.c)
+2. [Find sum of digits of a number](sumDigits.c)
+3. [do...while loop](doWhile.c)
+4. [Infinite loops](infiniteLoop.c)
+
+## Nested loops
+1. [Multiplication table using nested loops](nestedLoops.c)

Day 6/doWhileLoop.c

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+/*
+ * Program to add numbers entered by users
+ * as long as -1 is not entered
+ * using do while loop.
+ */
+
+#include <stdio.h>
+
+int main () {
+
+	int n = 0; // variable which is input by the user
+	int sum = 0;
+	do {
+		sum += n;
+		// do body
+		scanf("%d", &n);
+	} while (n != -1) ;
+
+	printf("%d\n", sum);
+
+	// Dry run:
+	// sum += 0
+
+	// User enters n = 1
+	// n != -1 => True
+	// sum += 1 
+
+	// User enters n = 2
+	// n != -1 => True
+	// sum += 2
+
+	// User enters n = -1
+	// n != -1 => False
+	// go outside the loop, we don't add -1 now!
+	return 0;
+}

Day 6/infiniteLoop.c

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+/*
+ * Program to write infinite loops
+ */
+
+#include <stdio.h>
+
+int main () {
+
+	// infinite loop
+
+	/*
+	for (; ;) {
+		; // nothing to execute
+	}
+	*/
+
+	while (1) {
+		;
+	}
+
+	return 0;
+}

Day 6/nestedLoops.c

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+/*
+ * Program to print multiplication table
+ * of numbers from 1 to 10 
+ * using nested loops.
+ */
+
+#include <stdio.h>
+
+int main () {
+
+	/*
+		1 2 3 4  5  6  7  8  9  10
+		2 4 6 8  10 12 14 16 18 20
+		3 6 9 12 15 18 21 24 27 30
+		4 ...
+	*/
+
+	// what are we looping on?
+	// print the first multiples of all numbers in the first line
+	// print the second multiples of all numbers in the second line
+	// ...
+	// print the 10th multiple of all numbers in last line
+
+	// outer loop: we loop on the i-th multiple (i=1 to 10)
+	// inner loop: all numbers 
+	
+	return 0;
+}

Day 6/sumDigits.c

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+/*
+ * Program to find sum of digits of a number
+ * using while loop
+ */
+
+#include <stdio.h>
+
+int main () {
+
+	// input 1234
+	// 1+2+3+4 = 10
+
+	// basically, your brain does the following:
+	// sees all the digits in the number
+	// and adds them up one by one
+
+	// basically, to write a program
+	// we need to loop oer all the digits in the number
+	// and add them to the result variable
+
+	// How do find out a specific digit in the number?
+	// last digit => remainder when divided by 10
+	// 1234 % 10 => 4, add to result, result = 4
+	// 1234/10 = 123 (integer division)
+	// 123 % 10 => 3, add to result, result = 4+3 = 7
+	// 123/10 = 12
+	// 12 % 10 => 2, add to result, result = 7+2 = 9
+	// 12/10 = 1
+	// 1 % 10 => 1, add to result, result = 9+1 = 10
+	// 1/10 = 0 (stop at this point)
+
+	// Pseudo code:
+	// number as input
+	// result <- 0
+	// while (number > 0) 
+	//    find the last digit (number % 10)
+	//    add the last digit to the result (result += lastDigit)
+	//    divide number by 10 (number /= 10)
+	// print(result)
+
+	int number;
+	scanf("%d", &number);
+
+	int result = 0;
+	while (number > 0) {
+		// lastDigit is a local variable
+		int lastDigit = number % 10;
+		result += lastDigit;
+		number /= 10;
+	}
+
+	// line below won't work, the scope of variable
+	// is limited to the part where it is declared
+
+	// lastDigit is declared inside the while loop
+	// so it can't be accessed outside the while loop
+	// printf("%d", lastDigit);
+
+	printf("The sum of digits in the number is: %d\n", result);
+	return 0;
+}

Day 6/whileLoop.c

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+/*
+ * Program to multiply numbers from 1 to n
+ * using while loop
+ */
+
+#include <stdio.h>
+
+int main () {
+
+	// variable to store result
+	int result = 1;
+
+	int n;
+	scanf("%d", &n);
+
+	// Pseudo code:
+	// result <- 1
+	// number <- 1
+	// while (number <= n) 
+	//   multiply number to result
+	//   increment number by 1
+
+	int number = 1;
+	while (number <= n) {
+		result *= number;
+		number ++;
+	}
+
+	printf("The product of numbers from 1 to %d is: %d\n", n, result);
+	return 0;
+}