Question

I am writing a program to convert the lower case sentence into upper case. I also want the length of the string. I am doing it by (both) arrays and pointers. The program is as follows:-

/* Program to convert the lower case sentence in upper case sentence and also calculate the length of the string */
#include<stdio.h>
main()
{
    char fac='a'-'A',ch[20],*ptr,a[20];int i=0,count=0;
    ptr=ch;

    /* Changing case and printing length by using pointers */
    printf("Enter the required string");
    gets(ptr);
    while(*ptr!='\0')
    {
        *ptr+=fac;   // LINE #1
        ptr++;
        count++;
    }
    puts(ptr);
    printf("%d",count);

    /* Changing case by using arrays */
    printf("Enter the required string");
    gets(ch);
    while(ch[i]!='\0')
    {
        ch[i]+=fac;
        i++;
    }
    puts(ch);
return 0;
}

This program is working perfectly for printing the length ( in the pointer part ) and changing the case ( in the array part).The problem is case-conversion by pointers. I am under impression that LINE#1 increments the value stored at the pointer “ptr” by the required number ( 32 ). But nothing is happening on the screen. Why is this happening? Please help.

Answer 1

Look at your loop:

while(*ptr!='\0')
{
    ...
    ptr++;
    ...
}
puts(ptr);

You’ve incremented ptr until its value is the address of the nul terminator! So all you’re printing is an empty string.

Instead, store the initial value of ptr somewhere before the loop:

char *initial_ptr;
...
initial_ptr = ptr;
while(*ptr!='\0')
{
    ...
    ptr++;
    ...
}
puts(initial_ptr);