java - Math operations conditional statement - 


public class eval {     public static void main(string[] args) {          int operand1;         char exp1;         int operand2;          if (args.length != 3 ) {             system.err.println("*** program needs 3 arguements***");             system.err.println("usage: java eval int1 exp int2");             system.exit(1);         }          operand1 = integer.parseint(args[0]);          exp1 = args[1].charat(0);          operand2 = integer.parseint(args[2]);           system.out.print(args[0] + args[1] + args[2] + "=");          switch(exp1){             case('-'):                 system.out.println(operand1 - operand2);                 break;             case('+'):                 system.out.println(operand1 + operand2);                 break;             case('/'):                 system.out.println(operand1 / operand2);                 break;             case('*'):                 system.out.println(operand1 * operand2);                 break;             default:                 system.out.println(" error.invalid operator.");         }       }     }

this program mathematical operations. program can multiply integers, why happen? furthermore, why (usuage: java eval) part necessary -- doesn't work without it. there way avoid doing this? lastly why args necessary. i'm sorry many questions, don't want blindly write program no clear understanding of i'm doing. thank , once again sorry many questions!

the problem multiplication not in java, command line itself. * character special on command lines, escape in command line , should fine:

$ java eval 6 * 9 *** program needs 3 arguements*** usage: java eval int1 exp int2 $ java eval 6 \* 9 6*9=54

the args necessary here because java takes command line arguments , passes them program through main parameter args.

you must java eval because you're running program java -- jvm itself. first argument class containing main method run. other command line arguments passed args parameter of main.

the java tutorial on subject explains how command-line arguments work.


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