using if statements with a string of letters and user input - objective-c

Question

Helllo I am still new to programing and had a question about using if statements while using user input with the research I have conducted i can't seem to find what I am doing wrong?
Below is my posted simple multiplication calculator.
#import <Foundation/Foundation.h>
int main (int argc, const char * argv[]) {
int a ;
int b ;
int c ;
printf("\n");
printf("\n");
printf("Welcome to calculator");
printf("\n");
printf("\n");
printf("what would you like to choose for first value?");
scanf("%d", &a);
printf("\n");
printf("What would you like to input for the second value?");
scanf("%d", &b);
c = a * b;
printf("\n");
printf("\n");
printf(" Here is your product");
printf("\n");
NSLog(#"a * b =%i", c);
char userinput ;
char yesvari = "yes" ;
char novari = "no";
printf("\n");
printf("\n");
printf("Would you like to do another calculation?");
scanf("%i", &userinput);
if (userinput == yesvari) {
NSLog(#" okay cool");
}
if (userinput == novari) {
NSLog(#"okay bye");
}
return 0;
}

Answer 1

You are scanning the character incorrectly with %i and you need to compare them using strcmp. If you are looking for a string from the user you need to use %s and you need a character buffer large enough to hold the input.
Try this
//Make sure userinput is large enough for 3 characters and null terminator
char userinput[4];
//%3s limits the string to 3 characters
scanf("%3s", userinput);
//Lower case the characteres
for(int i = 0; i < 3; i++)
userinput[i] = tolower(userinput[i]);
//compare against a lower case constant yes
if(strcmp("yes", userinput) == 0)
{
//Logic to repeat
printf("yes!\n");
}
else
{
//Lets just assume they meant no
printf("bye!\n");
}

Answer 2

I think you are reading a char using the wrong format %i: scanf("%i", &userinput);
And I think it is a better to use #NSString instead of simple char (I am not even sure what will happen in ObjC if you write char a = "asd", since you are giving a char a char[] value) . In that case, since strings are pointers, you cannot use == to compare them. You could use isEqualToString or isEqualTo instead. If you are interested in the difference between the two, look at this post would help.

Answer 3

In C, you can't compare strings using ==, so you would have to use a function like strcmp(), like this:
if ( !strcmp(userinput, yesvari) ) {
//etc.
}
The bang (!) is used because strcmp() actually returns 0 when the two strings match. Welcome to the wonderful world of C!