Add Day 5: Loops

Author: sahilbansal17

Day 5/README.md

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+## Getting started with Loops
+
+1. [Why do we need loops?](loopMotivation.c)
+2. [For loop](forLoop.c)
+3. [Exercise based on for loop](exerciseForLoop.c)

Day 5/exerciseForLoop.c

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+/*
+ * A simple execise based on for loop
+ */
+
+#include <stdio.h>
+
+int main () {
+
+	int n;
+	for (n = 9; n != 0; n --) {
+		printf("%d ", n--);
+	}
+
+	/* When the test condition evaluates to false
+	 * the loop stops
+	 */
+
+	/* Dry run: helps get a better idea
+	/* For loop:
+		1. Perform the initialization: n = 9
+		2. Peform the check, n != 0 TRUE
+		3. First execute the loop body
+		   Print n-- (Postfix unary decrement) 
+		   [postfix: use and update]
+		   [prefix: update and use]
+		   First the value of n is used, then updated
+		   9 is printed
+		   n = 8
+		4. The loop update statement is executed
+		   n = 7
+		5. 7 is printed
+		   n = 6 (from the loop body)
+		   n = 5 (from the loop update statement)
+		6. 5 is printed
+		7. 3 is printed
+		8. 1 is printed
+		   n = 0 (from the loop body)
+		   n = -1 (from the loop update)
+		9. n != 0 condition is checked, it evalues to true
+		   n is negative
+		   Its always going to decrement
+		   Loop never stops.....
+		   INFINITE LOOP!!!!!!!
+	*/
+	return 0;
+}

Day 5/forLoop.c

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+/*
+ * Program to sum numbers from 1 to n.
+ */
+
+#include <stdio.h>
+
+int main () {
+
+	int n;
+	printf("Please enter the value of n: ");
+	scanf("%d", &n);
+
+	int sumNumbersFrom1toN = 0;
+
+	// pseudo code:
+	// result = 0
+	// for number = 1 to n
+	//   result = result + number
+	// result now gives you the sum of numbers from 1 to n
+
+	/* 
+	 * Syntax to use a for loop:
+	 * for (initialization ; test expression; update expression) {
+	 *		// block of statements
+	 *	}
+	 */
+
+	for (int number = 1; number <= n; number += 1) {
+		// sumNumbersFrom1toN = sumNumbersFrom1toN + number
+		sumNumbersFrom1toN += number;
+	}
+
+	/*
+	 * Dry run:
+	 * Let's say user enters n = 3
+	 * sumNumbersFrom1toN = 0
+	 * For LOOP:
+	 *   number <- 1 // number is initialized to 1
+	 *   number <= 3 // condition is true
+	 *   // first the loop body is executed, then the update statement is executed
+	 *   sumNumberFrom1toN <- 0 + 1 = 1
+	 *   // loop body has finished
+	 *   number = number + 1
+	 *   number = 2
+	 *   // next iteration of loop starts
+	 *   number <= 3, yes it is true
+	 *   sumNumbersFrom1toN <- 1 + 2 = 3
+	 *   number = number + 1 = 3
+	 *   // next iteration of the loop
+	 *   number <= 3, true
+	 *   sumNumberFrom1toN <- 3 + 3 = 6
+	 *   number = number + 1 = 4
+	 *   // next iteration of the loop
+	 *   number <= 3, NOW THE CONDITION IS FALSE
+	 *   you go out of the loop
+	 */
+
+	printf("The sum of numbers from 1 to %d: %d\n", n, sumNumbersFrom1toN);
+
+	return 0;
+}

Day 5/loopMotivation.c

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+/*
+ * Program to print numbers from 1 to 10 to the screen
+ */
+
+#include <stdio.h>
+
+int main () {
+
+	/*
+	printf("1\n");
+	printf("2\n");
+	printf("3\n");
+	printf("4\n");
+	printf("5\n");
+	printf("6\n");
+	printf("7\n");
+	printf("8\n");
+	printf("9\n");
+	printf("10\n");
+	*/
+
+	// variable to store the number printed to the screen
+	int number = 1;
+
+	// loop entry bounded by a condition
+	// entry controlled loop, the condition is checked
+	// before running the loop for the first time
+	while (number <= 10) {
+		// once you enter the loop
+		// execute the loop body
+
+		printf("%d\n", number);
+
+		// update the value of number
+		number += 1;
+	}
+
+	return 0;
+}