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help understanding the code

post #1 of 4
Thread Starter 
hey can someone help explain this code function?

int compare_string(char *str1, char *str2)
{
int count = 1;

while(*str1==*str2)
{
if ( *str1 == '\0' || *str2 == '\0' )
break;

str1++;
str2++;
count++;
}
if( *str1 == '\0' && *str2 == '\0' )
return 0;
else
return count;
}
post #2 of 4
What don't you understand about it?

Here's the code indented for readability:
Code:
int compare_string(char *str1, char *str2)
{
        int count = 1;
        
        while(*str1==*str2)
        {
                if ( *str1 == '\0' || *str2 == '\0' )
                        break;

                str1++;
                str2++;
                count++;
        }
        if( *str1 == '\0' && *str2 == '\0' )
                return 0;
        else
                return count;
}
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#well
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post #3 of 4
Quote:
Originally Posted by gonX View Post

What don't you understand about it?

Here's the code indented for readability:
Code:
int compare_string(char *str1, char *str2)
{
        int count = 1;
        
        while(*str1==*str2)
        {
                if ( *str1 == '\0' || *str2 == '\0' )
                        break;

                str1++;
                str2++;
                count++;
        }
        if( *str1 == '\0' && *str2 == '\0' )
                return 0;
        else
                return count;
}

Phew! smile.gif


--

Anyway, the function, given two pointers to a C-string, checks each character of each until it reaches the end of one of the strings, at which point the loop stops. As all C-strings should be terminated with a zero (null termination), once we reach the termination we know we are at the end of the string.

While the end of each string has not yet been reached and the current character of the first and second strings match, the loop increments each string pointer by one (so that the next loop iteration checks the next character in each string) and also increments a count variable which is used in the return value of the function to tell the position of the first different character, if the strings differ at all.

If by the time the loop has finished and both strings have reached the end, then both strings are considered equal and the function returns 0 (comparison functions return 0 if the two items match). Otherwise, the function returns the position of the first different character, thus greater than zero, signalling that the two strings are not the same.
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Ol' Sandy
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"Zeus"
(12 items)
 
Elite Preview
(6 items)
 
CPUMotherboardGraphicsRAM
Intel Xeon E3-1230v3 Gigabyte GA-Z97X-UD5H-BK MSI Gaming GTX 980 Kingston 32GB (4x8) 
Hard DriveHard DriveHard DriveHard Drive
Plextor PX-256M5S 256GB Samsung EVO 1TB Hitachi HDS721010CLA332 Hitachi HDS723020BLA642 
Hard DriveHard DriveHard DriveOptical Drive
Hitachi HDS723020BLA642 Hitachi HUA722010CLA330 WDC WD10EARS-00Z5B1 TSSTcorp CDDVDW SH-S223B 
CoolingCoolingOSMonitor
Phanteks PH-TC14PE with TY-140's Lamptron FCv5 (x2) Windows 8 Pro 64-bit Dell U2412M 
MonitorMonitorMonitorKeyboard
Dell U2412M Dell U2212HM Dell U2713HM Topre Realforce 87UB | Ducky DK9087 G2 Pro 
PowerCaseMouseMouse Pad
Corsair AX-750 Corsair Obsidian 650D Logitech G700 XTRAC Ripper XXL 
AudioAudioAudioAudio
Beyerdynamic DT-770 Pro 250ohm Schiit Bifrost DAC Schiit Asgard 2 HiVi Swan M50W 2.1 
CPUMotherboardRAMHard Drive
Intel Xeon E5-2620 Super Micro X9SRL-F-B 128GB 1333MHz LSI 9271-8i 
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VMware ESXi 5.5 SeaSonic SS-400FL2 Fractal Define R3 
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post #4 of 4
Thread Starter 
Oh, thanks
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