Pointers

Source Code from Notes

Example

Example program to read in two numbers from the command line and add them together. 


#include <iostream.h>
#include <stdlib.h>

main(int argc,char *argv[])
{
        float           a,b,answer;

        // ensure correct number of arguments 
        if (argc != 3)
        {
                cout << "Wrong number of arguments for program\n";
                exit(1);
        }


        /* convert argument string to float */
        a = atof(argv[1]);
        b = atof(argv[2]);

        answer = a + b;
        cout << "Answer = " << answer << "\n";
}

Example

This example is more complex and is for a program which requires a flag to indicate what operation should be performed on the two numbers. The flags are indicated by the minus (-) sign. 

#include <iostream.h>
#include <stdlib.h>

main(int argc,char *argv[])
{
        int     add_flag = 1;
        int     sub_flag = 0;
        int     mult_flag = 0;
        float   a,b;

        argc--;
        argv++;

        while ((argc > 0)&&(**argv == '-')){
                switch(*++*argv){
                        case 'a' : // add 
                                   add_flag = 1;
                                   break;
                        case 's' : // subtract 
                                   sub_flag = 1;
                                   add_flag = 0;
                                   break;
                        case 'm' : // multiply 
                                   mult_flag = 1;
                                   add_flag = 0;
                                   break;
                        default  : cout << "Unknown flag\n";
                                   exit(1);
                }
                argc--;
                argv++;
        }

        if (argc != 2)
        {
                cout << "Wrong number of arguments for program\n";
                exit(1);
        }

        a = atof(argv[0]);
        b = atof(argv[1]);

        if (add_flag == 1)
                cout << "answer = " << a+b << "\n";
        else if ( mult_flag == 1)
                cout << "answer = " << a*b << "\n";
        else if (sub_flag ==1)
                cout << "answer = " << a-b << "\n";

}

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