Does if-structure in C affect the value of variable?

Question

Im trying to write a simple C program to convert the cases of letters

char a;
a = getchar();
if(a<=90&&a>=65)
    putchar(a+32);
else if(a<=122&&a>=97)
    putchar(a-32);
else
    putchar(a);

When the input is 'A' or 'c',the output is correct;however,when it comes to 'g',the output becomes space and when entering numbers and signals,only get a different output instead of itself.Then I changed the order of ifs,the second problem was solved but the 'g' problem remains.

But I thought the if-structure wouldnt change the value of a;Im quite confused and wonder how.

Answer 1

The function getchar reads all symbols including white spaces from the input stream.

Use instead

scanf( " %c", &a );

Also it is a bad idea to use magic numbers like for example 65 or 32.

Here is a demonstrative program

#include <stdio.h>

int main(void) 
{
    char c;

    while ( scanf( " %c", &c ) == 1 )
    {
        if ( 'A' <= c && c <= 'Z' )
        {
            putchar( c | ' ' );
        }
        else if ( 'a' <= c && c <= 'z' )
        {
            putchar( c & ~' ' );
        }
        else
        {
            putchar( c );
        }
    }

    return 0;
}

If to enter for example

A
a
1
G
g
2

then the program output will be

aA1gG2

If to use getchar then the approach can look the following way

#include <stdio.h>
#include <ctype.h>

int main(void) 
{
    int c;

    while ( ( c = getchar() ) != EOF )
    {
        if ( 'A' <= c && c <= 'Z' )
        {
            putchar( c | ' ' );
        }
        else if ( 'a' <= c && c <= 'z' )
        {
            putchar( c & ~' ' );
        }
        else if ( isgraph( ( unsigned char )c ) )
        {
            putchar( c );
        }
    }

    return 0;
}