Problem in a program to convert upper case string to lowercase using function in C

Question

I am trying to write a program which will only compare same case letter, but first it should convert any case to a particular case.

But I am having trouble converting the string to any particular case using a function, though I have figured out how to do that without a function. Here's my code. Can anyone help me find out where I am going wrong?

#include<stdio.h>
#include<string.h>
void order(char input[])
{
    int i=0;

    while(input[i]!='\0')
    {
        if(input[i]>'65' && input[i]<'92')
        {
            input[i]+=32;
           // printf("WORKING\n");
        }

        i++;

    }
}
int main()
{
    char input1[101], output1[101];
    char input2[101], output2[101];
    int r;

    scanf("%s",tolower(input1));
    scanf("%s",input2);

    order(input1);
    order(input2);

    printf("%s\n",input1);
    printf("%s\n",input2);

    /*

    r=strcmp(output1,output2);


    if(r<0)
        printf("-1\n");
    else if(r>0)
        printf("1\n");
    else
        printf("0\n");

    */

}

Answer 1

Change this:

if(input[i]>'65' && input[i]<'92')

to this:

if(input[i] >= 65 && input[i] <= 90)

since you want to check for the ASCII codes of A and Z. Notice that because you used magic numbers, you made a mistake for both. I had to check an ASCII table to figure that out that you needed the equality sign as well, and 90 (code for Z), instead of 92 (code for '\\').

I suggest you then to use characters constants, like this:

if(input[i] >= 'A' && input[i] <= 'Z')

Answer 2

Constant and off-by-1 errors.

• '65' is a multi byte constant and certainly 65 was meant. @gsamaras . ASCII Z is 90.

   // if(input[i]>'65' && input[i]<'92') if(input[i]>65 && input[i]< Zee) 

• Off by 1 due to > vs. >=

   // if(input[i]>'65' && input[i]<'92') // if(input[i]>65 && input[i]< Zee) if(input[i] >= 65 && input[i] <= 90) 

---

Character constants are more self documenting. Consider 'A'

    if(input[i] >= 'A' && input[i] <= 'Z')

Ideally code would use standard C library functions to detect case.

    if(isupper((unsigned char) input[i]))

Yet code could call toupper() directly and skip the if() .

while(input[i]) {
  input[i] = tolower((unsigned char) input[i]);
  i++;
}

// or 

for (size_t i = 0; input[i]; i++) {
  input[i] = tolower((unsigned char) input[i]);
}

Answer 3

You're trying to pass a char* to the tolower in scanf("%s",tolower(input1)); .

Change it to scanf("%s", input1);

c - convert a mixed-case string to all lower case should tell you how to convert a string to lower case.

Take a look at https://linux.die.net/man/3/tolower and https://linux.die.net/man/3/toupper .