toupper tolower not working , help what's wrong with my code

Question

main.cpp

#include <iostream>
#include "Module2.h"

int main()
{
std::cout<<"This is a test of Module2.h"<<std::endl;
std::cout<<UCase("This is a test of UCase")<<std::endl;
std::cout<<LCase("This is a test of LCase")<<std::endl;
system("pause");
return 0;

}

Module2.h

#include <iostream>
#include "Module2.h"

int main()
{
std::cout<<"This is a test of Module2.h"<<std::endl;
std::cout<<UCase("This is a test of UCase")<<std::endl;
std::cout<<LCase("This is a test of LCase")<<std::endl;
system("pause");
return 0;

}

Module2.cpp

///////////////////////////////////////////////////
//Module : Module2.cpp
//
//Purpose : Shows the usage of modular functions
///////////////////////////////////////////////////

#include "Module2.h"

///////////////////////////////////////////////////
//UCase()

char *UCase(char *str)
{
//convert each char in  the string to uppercase
//
int len = strlen(str);
for ( int i ; i < len ; i++)
{
    std::cout<<"In UCase"<<std::endl;
     str[i]=toupper(str[i]);
}

return str;
}

///////////////////////////////////////////////////
//LCase()

char *LCase(char *str)
{
//convert each char in  the string to uppercase
//
int len = strlen(str);
for ( int i ; i < len ; i++)
{
    std::cout<<"In LCase"<<std::endl;
    str[i]=tolower(str[i]);
}  
return str;
}

When I run it there is no warning or error . But , it don't upper and lower the string . I have thought my for loops are wrong , but it seems to be right . What's wrong with my code.

If this compiled without warnings, you need to enable more warnings. — Baum mit Augen, Jan 26 '15 at 23:03
Are you sure your "Module2.h" is really what you posted, identical to "main.cpp"? — Deduplicator, Jan 26 '15 at 23:05
You have two main() functions. Only one is allowed: this is where the program is supposed to start — Bérenger, Jan 26 '15 at 23:05
@goInDoor Depends on the compiler. For gcc or clang, add the option -Wall — Bérenger, Jan 26 '15 at 23:35
Also, is there a specific reason for not using std::string ? — Bérenger, Jan 26 '15 at 23:36

score 2 · Accepted Answer · edited May 23 '17 at 12:14

The main problem is that you are trying to modify string literals such as "This is a test of UCase". This is undefined behaviour. You need to copy the literals into a char array that you can modify.

Also note that binding char* to a string literal is deprecated and forbidden, for good reason. This should have emitted a warning:

UCase("This is a test of UCase") // not good: binding char* to literal

There are other problems with your code: undefined behaviour (UB) in loops with uninitialized variables,

for ( int i ; i < len ; i++) // using uninitialized i: UB

You should also have a look at toupper and tolower documentation. They both accept int with some restrictions on their values. You have to ensure you don't pass a value that causes undefined behaviour, bearing in mind that char can be signed. See for example Do I need to cast to unsigned char before calling toupper?

And anyway, `tolower` and `toupper` aren't really suitable for changing case. Only nearly, under some locales. — Deduplicator, Jan 26 '15 at 23:07
@BaummitAugen I added something about other problems in the code. Not sure it is worth spending the time on this crap. — juanchopanza, Jan 26 '15 at 23:11

score 1 · Answer 2 · answered Jan 26 '15 at 23:06

1

Loops like this one have undefined behavior:

for ( int i ; i < len ; i++)

The reason is that you did not start i at value 0.
You have no idea what value i starts at!
It could be -10, could be 824.

If you want a value to be initialized, you have to initialize it.
I suggest:

for (int i=0; i < len; i++)

answered Jan 26 '15 at 23:06

abelenky

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for(int i=0 ; i – goInDoor Jan 26 '15 at 23:12
2

@goInDoor The idea is that you fix *all the errors*. – juanchopanza Jan 26 '15 at 23:14

goInDoor · Answer 3 · 2015-01-27T02:55:07.943

char *UCase( char *str)
{
char ch;
int i=0;

while(str[i])
{
    ch=str[i];
    putchar(toupper(ch));
//putchar : The value is internally converted to an unsigned char when written.
    i++;
}
}

///////////////////////////////////////////////////
//LCase()

char *LCase(char *str)
{
char ch;
int i=0;

while(str[i])
{
    ch=str[i];
    putchar(tolower(ch));
    i++;
}
}

I finally write this . Although , I still not quite understand , but I learned

#include <ctype.h>
int tolower( int ch );

means tolower toupper can change only one character each time , so I can not

tolower ("This is a test of LCase");

code like this .

toupper tolower not working , help what's wrong with my code

3 Answers3