Objective-C programming language allows to use one loop inside another loop. Following section shows few examples to illustrate the concept.
The syntax for a nested for loop statement in C is as follows −
for ( init; condition; increment ) { for ( init; condition; increment ) { statement(s); } statement(s); }
The syntax for a nested while loop statement in Objective-C programming language is as follows −
while(condition) { while(condition) { statement(s); } statement(s); }
The syntax for a nested do...while loop statement in Objective-C programming language is as follows −
do { statement(s); do { statement(s); } while( condition ); } while( condition );
A final note on loop nesting is that you can put any type of loop inside of any other type of loop. For example, a for loop can be inside a while loop or vice versa.
The following program uses a nested for loop to find the prime numbers from 2 to 100 −
#import <Foundation/Foundation.h> int main () { /* local variable definition */ int i, j; for(i=2; i<100; i++) { for(j=2; j <= (i/j); j++) if(!(i%j)) break; // if factor found, not prime if(j > (i/j)) NSLog(@"%d is prime\n", i); } return 0; }
When the above code is compiled and executed, it produces the following result −
2013-09-07 22:40:01.004 demo[1027] 2 is prime 2013-09-07 22:40:01.005 demo[1027] 3 is prime 2013-09-07 22:40:01.005 demo[1027] 5 is prime 2013-09-07 22:40:01.005 demo[1027] 7 is prime 2013-09-07 22:40:01.005 demo[1027] 11 is prime 2013-09-07 22:40:01.005 demo[1027] 13 is prime 2013-09-07 22:40:01.005 demo[1027] 17 is prime 2013-09-07 22:40:01.005 demo[1027] 19 is prime 2013-09-07 22:40:01.005 demo[1027] 23 is prime 2013-09-07 22:40:01.005 demo[1027] 29 is prime 2013-09-07 22:40:01.005 demo[1027] 31 is prime 2013-09-07 22:40:01.005 demo[1027] 37 is prime 2013-09-07 22:40:01.005 demo[1027] 41 is prime 2013-09-07 22:40:01.005 demo[1027] 43 is prime 2013-09-07 22:40:01.005 demo[1027] 47 is prime 2013-09-07 22:40:01.005 demo[1027] 53 is prime 2013-09-07 22:40:01.005 demo[1027] 59 is prime 2013-09-07 22:40:01.005 demo[1027] 61 is prime 2013-09-07 22:40:01.005 demo[1027] 67 is prime 2013-09-07 22:40:01.005 demo[1027] 71 is prime 2013-09-07 22:40:01.005 demo[1027] 73 is prime 2013-09-07 22:40:01.005 demo[1027] 79 is prime 2013-09-07 22:40:01.005 demo[1027] 83 is prime 2013-09-07 22:40:01.005 demo[1027] 89 is prime 2013-09-07 22:40:01.005 demo[1027] 97 is prime