DMP - Chapter 6

Looping - for, while, do while

• while loop

  #include <stdio.h>
  
  void main(void)
  {
  	long num;
  	long sum = 0L;
  	int status;
  
  	printf(Enter integer to be summed (enter q to quit: ");
  	status = scanf("%ld", &num);
  	while (status == 1)	
  	{
  		sum = sum + num;
  		printf("enter next number (q to quit): ");
  		status = scanf("%ld", &num);
  	}
  	printf("Sum is: %ld\n", sum);
  }
  
  Variation: while(scanf("%ld", &num) == 1)
  
  

• What's wrong?

  index = 1;
  while (index < 5)
  	printf("Bonjour!\n");
  
  index = 1;
  while (--index < 5)
  	printf("Bonjour!\n");
  
  index = 10;
  while (index++ < 5)
  	printf("Bonjour!\n");
  
  index = 3;
  while (index < 5)
  	printf("Bonjour!\n");
  	index++;
  
  index = 3;
  while (index++ < 5);
  	printf("Bonjour!\n");
  
  

• Relational operators: <, <=, ==, >=, >, !=
• Everything is True except zero.
• Operator precedence:

  ()
  - + ++ -- sizeof (all unary) 	R-L
  * / % 				L-R
  + -				L-R
  < > <= >=			L-R
  == !=				L-R
  =				R-L
  

• for loop

  #include >stdio.h>
  #define NUMBER 22
  
  void main(void)
  {
  	int count;
  	for (count = 0; count < NUMBER; count++)
  		printf("Hit me!\n");
  }
  

• +=, -=, *=, /=, %=
  • for (count = NUMBER; count > 0; count--)
  • for (count = 0; count < NUMBER; count += 5)
  • for (ch = 'a'; ch <= 'z'; ch++)
  • for (num = 1; num * num * num < NUMBER; num++)
  • for (num = 1.234; num < NUMBER; num *= 1.2)
  • for (x = 2; y < NUMBER; y = (++x * 3 - 2) / 2)
  • for (count = 0; count < NUMBER;) count++;
  • for (;;)
  • for (initialize; test; update)
• comma operator (left-to-right order)
• do while:

  void main(void)
  {
  /*********** exit condition loop ***********/
  	do
  	{
  		scanf("%c", &ch);
  		printf("%c", ch);
  	}while (ch != '#');
  
  /*********** entry condition loop ***********/
  	scanf("%c", &ch);
  	printf("%c", ch);
  	while (ch != '#')
  	{
  		scanf("%c", &ch);
  		printf("%c", ch);
  	}
  }
  

• Nested loops

  #define NUM1 3
  #define NUM2 2
  
  for (i = 0; i < NUM1; i++)
  	for (j = 0; j < NUM2; j++)
  		printf("%d %d\n", i, j);
  

• Arrays (subscripts, indices, or offsets)
• Power function

  double power(double a, int b)
  {
  	double pow = 1;
  	int i;
  
  	for (i = 0; i < b; i++)
  		pow *= a;
  	return(pow);
  }
  

• Review:
  • Values?

    		int quack = 2;
    		quack += 5;
    		quack *= 10;
    		quack -= 6;
    		quack /= 8;
    		quack %= 3;
    	

  • Errors?

    	int main(void)
    	{
    		int i, j, list(10);
    	
    		for (i = 1, i <=10, i++)
    		{
    			list[i] = 2 * i + 3;
    			for (j = 1, j >= i, j++)
    				printf("%d\n", list[j]));
    	}
    	

  • Output?

    	void main(void)
    	{
    		int i = 0;
    
    		while (++i < 4)
    			printf("Bonjour ");
    		do
    			printf("Au revoir ");
    		while (i++ < 8)
    	}
    
    	void main(void)
    	{
    		int i;
    		char ch;
    
    		for (i = 0, ch = 'A'; i < 4; i++, ch += 2 * i)
    			printf("%c", ch);
    	}
    
    	
    	
    	
    

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  Assignment #5: Due Oct. 15, 1995.

  p.202-3: #2, 3, 4, 5, 9

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  For comments or questions email to: ich@peabody.jhu.edu static int *vals = {2, 3, 4,5,6,7};