CS 102
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The for loop

The discussion below uses the following Multiplication Tables Examples:

The for loop gives us the same functionality as a while loop, with a more convenient way to keep track of loop counting variables. The general format is: 

for (initialize; endingCondition; postLoopUpdate) {
	action;
}

The initialize code is performed the first time only. Then endingCondition is checked. If it is true, the action(s) inside the loop are exectued. After the code in the loop is executed, the postLoopUpdate code is executed. The endingCondition is again checked, and the code in the loop is again executed, and so on, until the endingCondition is false.

Multiplication Tables Examples

Before studying the following examples, take a look at the example programs describing the use of cin and cout for input and output. The first one is a simple example, and the second one combines cin and cout with scanf and printf.

Consider the following examples, found in the course account at examples/other/multiplication. The first one shows how to display a multiplication list for a single number. For instance, selecting 3 would then display in a column the values 3, 6, 9, 12, 15, 18, ... and so on up to 36, which is 3 times 12. Using a while loop, this looks like: 
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// mult1.c - display mult. table from 1 - 12 for a #
#include <iostream.h>

main()
{
   int base,counter;

   cout<<"Please enter the base: ";
   cin>> base;

   //Now display the output
   counter=1;
   while (counter <= 12) {
      cout<< counter * base<<"\n";
      counter++;
   }
}

(Note: be sure to have looked at the notes on cin and cout before looking at this example.) The equivalent using a for loop instead of a while loop is: 
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// mult2.c - display mult. table from 1 - 12 for a # using for
#include <iostream.h>

main()
{
   int base,counter;

   cout<<"Please enter the base: ";
   cin>> base;

   //Now display the output
   for (counter=1; counter <=12; counter++) {
      cout<< counter * base<<"\n";
   }
}

And more involved: 
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// mult3.c - display mult. table from start - end for a #
#include <iostream.h>

main()
{
   int base,counter;
   int start, end;    //Loop range values

   cout<<"Please enter the base, starting position, ending position: ";
   cin>> base >> start>> end;

   //Now display the output
   for (counter=start; counter <=end; counter++)
      cout<< counter * base<<"\n";
}

And even more involved: 
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// mult4.c - display some rows of a mult. table from
//                 firstRow to lastRow, displaying columns
//                 up until the numColumns.

#include 

main()
{
   int i, j, firstRow, lastRow, numColumns;

   printf( "Please enter 3 integers for a multiplication table, \n ");
   printf( "where the first two are the start and end rows,\n ");
   printf( "and the third is the last column: ");
   scanf("%d %d %d", &firstRow, &lastRow, &numColumns);

   // Each loop iteration displays a row
   for( i=firstRow; i<=lastRow; i++) {
      // loop to display contents within each row
      for( j=1; j<=numColumns; j++) {
         printf("%4d", i*j);
      }
      printf("\n");
   }
}



[CS Dept] [UIC] [Prof. Reed]