CGS 3460

Program loopingProgram looping Why we need loop

Make code concise for repetitive processes

When to use loop Run a block of code repetitively Process multiple data using same procedure

How to use loop for while do

     

CGS 3460

Example – Calc Factorial Example – Calc Factorial Goal: computing factorial N (N!)

F(N) = N! = 1 * 2 * 3 * …… N Fact

F(1) = 1;

F(2) = 1 * 2 = F(1) * 2;

F(3) = 1 * 2 * 3 = F(2) * 3; …

F(N) = 1 * 2 * … * N = F(N-1) * N;

     

CGS 3460

Example – Calc Factorial (cont.)Example – Calc Factorial (cont.)F(N) = F(N-1) * N;

F = F * M;

F = 1; M = 1;

M = M +1;When to stop?

M equals to N

     

CGS 3460

Calc Factorial – Data FlowCalc Factorial – Data FlowF(N) = F(N-1) * N;

Initial setting:

M = 1; F = 1; Main calculation

F = F * M; Stop criteria

M = N What else

increase M by 1

M = M + 1;

F = F * M;

F = 1; M = 1;

M = M +1;

     

CGS 3460

Flow Chart ComponentsFlow Chart Components Help to document program logic

* Not required.

     

CGS 3460

Calc Factorial – Flow chartCalc Factorial – Flow chartF(N) = F(N-1) * N;

Initial setting:

M = 1; F = 1; Main calculation

F = F * M; Stop criteria

M = N What else

increase M by 1

M = M + 1;

     

CGS 3460

for loopfor loop Format: for( init_expression; loop_condition; loop_expression )

{ program statement; }

Flow:

Condition satisfied?

No

Initial Expression

Yes

Program statement

loop expressionloop expression

     

CGS 3460

Calculate factorialCalculate factorialfor( init_expression; loop_condition; loop_expression )

{ program statement; }

Correspondingly when F(N)init_expression:

loop_condition:

loop_expression:

program statement:

M = 1;

M <= N;

M = M + 1;

F = F * M;

     

CGS 3460

Calc Factorial – codeCalc Factorial – code#include <stdio.h>

int main(void){

int F, N, M;

F = 1;N = 10;

for(M=1; M<=N; M=M +1){ F = F * M;}printf(“result is: %i \n”, F);return 0;

}

     

CGS 3460

init_expressioninit_expression Set initial values before the loop begins

Can be multiple valid C program statements, separated by comma (,)

for( i = 0, j = 0; i < 10; ++i ) May be omitted if initial values have been set before

• Make sure to put an empty statement with only semicolon (;)

for(; i<10; i++) Declaring variables in the loop

     

CGS 3460

loop_expressionloop_expression Change values after the program statements in the for

loop Can be multiple valid C program statements, separated by comma (,)

for(i = 0; i < 10; j++,++i ) May be omitted

• put nothing

for(; i<10; )• Make sure the value for i has been changed within the for loop!

     

CGS 3460

loop_conditionloop_condition Relational expression stating when loop continues

Operator Meaning Example

== Equal to Count == 10

!= Not equal to Count != 10

< Less than Count < 10

<= Less than or equal to Count <= 10

> Greater than Count > 10

>= Greater than or equal to Count >= 10

     

CGS 3460

loop_condition – exampleloop_condition – exampleWhat is the value of count after the for loop?

for(count = 1;count == 5; count++) { … }

count1

Loop condition satisfied?no

     

CGS 3460

loop_condition – exampleloop_condition – exampleWhat is the value of count after the for loop?

for(count = 1;count != 5; count++) { … }

count12345

Loop condition satisfied?YesYesYesYesno

     

CGS 3460

loop_condition – exampleloop_condition – exampleWhat is the value of count after the for loop?

for(count = 1;count < 5; count++) { … }

count12345

Loop condition satisfied?YesYesYesYesno

     

CGS 3460

loop_condition – exampleloop_condition – exampleWhat is the value of count after the for loop?

for(count = 1;count <= 5; count++) { … }

count123456

Loop condition satisfied?YesYesYesYesYesno

     

CGS 3460

loop_condition – exampleloop_condition – exampleWhat is the value of count after the for loop?

for(count = 1;count > 5; count++) { … }

count1

Loop condition satisfied?no

     

CGS 3460

loop_condition – exampleloop_condition – exampleWhat is the value of count after the for loop?

for(count = 1;count >= 5; count++) { … }

count1

Loop condition satisfied?no

     

CGS 3460

loop_condition – examplesloop_condition – examples1. for(count = 1; count == 5; count++) { … }

2. for(count = 1; count != 5; count++) { … }

3. for(count = 1; count <5; count++) { … }

4. for(count = 1; count <=5; count++) { … }

5. for(count = 1; count >5; count++) { … }

6. for(count = 1; count >=5; count++) { … }

What is the value of count after the for loop?

1 2 3 4 5 6

count 1 5 5 6 1 1

     

CGS 3460

Nested for LoopsNested for Loops Insert a loop within the loop of another

for( i=1; i<10; i++)

{

for(j=1; j<10; j++)

{

…;

}

…;

}

     

CGS 3460

ExampleExample If we want to print following pattern*

**

***

****

*****

******

*******

********

*********

**********

Print n stars at the nth line

Print 1 star at the 1st line

Print 2 stars at the 2nd line

Print 3 stars at the 3rd line

     

CGS 3460

CodeCode#include <stdio.h>

int main(void)

{

int row, col;

for (row = 1; row <= 5; row++)

{

for (col = 1; col <= row; col++)

{

printf("*");

}

}

}

printf("\n");

     

CGS 3460

Print Factorial F(1) … F(10)Print Factorial F(1) … F(10)#include <stdio.h>

int main(void){ int F, N, M;

F = 1; //variable that holds the result N = 10; /*what to calculate the factorial of*/

printf("num \t factorial \n"); for(M=1; M<=N; M=M+1) { F = F * M; printf("%i \t %i \n", M, F); }

return 0;}

     

CGS 3460

Calculate Fibonacci Numbers(0, 1, 1, 2, 3, 5, 8, 13, …)

Calculate Fibonacci Numbers(0, 1, 1, 2, 3, 5, 8, 13, …)

initial value:

init_expression:

loop_condition:

loop_expression:

program statement:

N = 2;

N <= M;

N = N + 1;

Fn = Fnm1 + Fnm2;

Fnm1 = 1; Fnm2 = 0;

What else? Fnm2 = Fnm1; Fnm1 = Fn;

     

CGS 3460

Pseudo codePseudo code

M = 6;

n;

Fn, Fnm1=1, Fnm2=0;

for(n = 2; n <= M; n++)

{

Fn = Fnm1 + Fnm2;

Fnm2 = Fnm1;

Fnm1 = Fn

}

n n <= M Fn Fnm2 Fnm1

* * * 0 1

2 T 1 1 1

3 T 2 1 2

4 T 3 2 3

5 T 5 3 5

6 T 8 5 8

7 F

     

CGS 3460#include <stdio.h>

int main(void) { int m = 0; int Fn = 0; int Fnm1 = 1; int Fnm2 = 0;

/* print out the first two numbers */ printf("F(%i) = %i\n", 0, 1); printf("F(%i) = %i\n", 1, 1); /* print out the next 38 numbers */ for (n = 2; n < 40; n++) { /* calculate the next number and print it */ Fn = Fnm1 + Fnm2; printf("F(%i) = %i\n", n, Fn); /* update the old two numbers for next time through the loop */ Fnm2 = Fnm1; Fnm1 = Fn; }

/* no error */ return 0; }