- If you want to repeat the same blocks of code over and over you have two choices. Copy

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1 2013/2014 Programming Fundamentals for Engineers Lab Lab Session # 4 Loops ALQUDS University Department of Computer Engineering Objective: 1. Study the benifits of using loops in programming. 2. Investigate for loop control statement. 3. Investigatethe while and do-while constructs. 4. Compare different looping constructs. Background - If you want to repeat the same blocks of code over and over you have two choices. Copy and paste each block or you can use a looping construct. - In C, there are three different types of looping constructs: for (the loop will usually be traversed a fixed number of times), while (repeating an action until an associated test returns false), and do-while (the test occurs after the loop body is executed the first time). Each of them has their own specific uses and syntax. Experiment 4.1 For Loops for( variable declaration/initialization; condition; variable update) //Code to be repeated The first part is the variable declaration/initialization. Here you can either declare a new variable and assign it a value or use an existing variable. In C you can use any integer based data type (int, char, etc ). Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 1

2 The Second part is the condition tells the program to exit the loop when the conditional expression evaluates to false. The third part is the variable(s) update(s) or operation(s) needed after each iteration. Generally you would put something like x++, x = x + 10, but if you really wanted to, you could call another function to update the variable. for loops are generally/usually used when you know the exact number of iterations (but not necessary). Step 1: Compile and execute this program and record the results below: int x; for (x = 0; x < 10; x++) printf("x = %d\n", x); What does this program do?. Step 2: modify the program in step1 to count down from Step 3: A common programming error is to place a semicolon (;) at the end of the line containing the opening statement of the for loop. Modify the program from Step 1 to include this error. for(x= 0; x < 10; x++); Compile and execute the program. Record the results.. Step 4: Explain the results from the program in Step Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 2

3 Experiment 4.2 Nested for loop Step 1: Compile and execute the program. for ( i = 0 ; i < n ; i ++) for ( j = 0 ; j < m ; j++) printf("*"); printf("\n"); Record the results with n=5, m=10 then comment the results. Step 2: Modify the program to be n=m=8, comment the results. Step 3: Modify the program in step 1 so it calculates and prints the multiplication table with n=m=10. Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 3

4 Experiment 4.3 while and do-while looping structures: while ( condition ) //Code to be repeated A while loop is basically a simple for loop with no initialization or update sections. The condition can be any Boolean expression and the loop will continue while the condition evaluates to true. Here are a couple of legal conditions: (x == 1), (x!= 7), or even (x ==5 v == 7) which says execute the loop while x is equal to 5 or v is equal to Equivalent for and while loops for (expression_1; expression_2; expression_3)...block of statements to execute... expression_1; while (expression_2)...block of statements... expression_3; All three expressions are optional (syntax-wise). First expression.. i = 10; for(;i > 0 ; --i) printf("i = %d", i); Third expression.. for (i = 0 ; i > 0 ;) printf(" I = %d", i--); First and Third expressions (as while loop).. i = 0; for(; i > 0 ;) printf("i = %d", i --); Same as.. i = 0; while( i > 0 ) printf("i = %d", i --); Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 4

5 do //Code to be repeated while (condition); do-while loops are essentially the same as while loops except that you know they ll be executed at least once. The condition again can be any Boolean expression and will loop while the condition is true. A do-while loop says Execute this block of code, and then continue to loop while the condition is true. Step 1: Predict the output of this program, which uses a while loop. int x = 5; while(x < 5) printf("x=%d",x); x++; printf("that's all folks!"); Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 5

6 Step 2. Predict the output of this program, which is similar to the program in Step 1, but uses a do-while loop instead of a while loop. int x = 5; do printf("x=%d",x); x++; while(x < 5); printf("that's all folks!"); Step 3. Explain the differences in the output between the two programs in Steps 1 and Step 4. Rewrite the following program segment using a do-while loop rather than a while loop. Your segment should produce the same output as the original while loop. int x = 5; while(x >0) printf("reduce!\nreuse!\nrecycle!\n"); x--; Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 6

7 Experiment 4.4 Step 1: Predict the output of this program, and record your comments. #include <time.h> #include <stdlib.h> srand(time(null)); int r = rand()%20; printf("a random number between 0 and 19: %d.\n", r); Step 2: Write a program that implements the game "Guess my number". After each guess respond with either "try higher", "try lower" or "You guessed it". To write this program, you will need toassign the target number a random value (form 1 to 100). Algorithm C program Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 7

8 Experiment 4.5 break and continue and goto The break command will exit the most-immediately-surrounding loop regardless of what the conditions of the loop are. The break does not work with if. It only works in loops and switches. A break can escape only one level of nesting, see next example while( ) switch( ) break; If you are executing a loop and hit a continue statement, the loop will stop its current iteration, update itself (in the case of for loops) and begin to execute again from the top. goto identifier;.. identifier: statement break and continue can jump forward, but goto can jump forward or backward. Step 1: Compile and execute the program. Record the results and comment the results. for (int x = 0; x < 10; x++) if(x == 1 x == 4 ) continue; else if(x == 8) break; else printf("x = %d.\n", x); Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 8

9 Step 2: Replace the statements: if(x == 1 x == 4) with if(x == 1 && x == 4), predicate the result, then test the new program. Post lab 4: 1. Write a C program that uses nested for loop, a loop inside of a loop, to print a 3x5 rectangle of asterisks (*). ***** ***** ***** 2. Replace the nested for loops in the previous problem with while loops. 3. Write a C program that asks the user to enter a fraction number then converts the fraction to its lowest terms. E.g. Enter a fraction: 9/15. The lowest term is: 3/5. Hint: One way to do it is to try and divide by the smallest of them (if both divisible), otherwise go down trying other numbers till 2, other solution could be based on finding the GCD first (there s an algorithm for that). Can you think of other solutions? 4. Write a program that prints a triangle with a user-entered number of rows. For example, if the user enters 4, the program should print one of the following triangles: A. * B. * C. **** D. **** ** ** *** *** *** *** ** ** **** **** * * 5. Write a C program that has the output below: Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 9