calculator problem

[darkphenom]

I have a problem with a calculator i was making. I could use some help because i get the following error:

calculator.c: In function ‘main’:
calculator.c:14: error: ‘a’ undeclared (first use in this function)
calculator.c:14: error: (Each undeclared identifier is reported only once
calculator.c:14: error: for each function it appears in.)
calculator.c:24: error: ‘s’ undeclared (first use in this function)
calculator.c:34: error: ‘m’ undeclared (first use in this function)
calculator.c:44: error: ‘d’ undeclared (first use in this function)

here is the code:

#include <stdio.h>

int main ()
{
char letter;
int num1;
int num2;
int answer;

printf("Enter <a> for addition \nEnter <s> for subtraction               \nEnter <m> for multiplication \nEnter <d> for division \nEnter:");

scanf("%c", &letter);

if (letter == a)
{
printf("Enter the two numbers you want to add");
scanf("%d", &num1);
scanf("%d", &num2);

answer = num1+num2;
printf("The answer is:%d", answer);
}

else if (letter == s)
{
printf("Enter the two numbers you want to subtract");
scanf("%d", &num1);
scanf("%d", &num2);

answer = num1-num2;
printf("The answer is:%d", answer);
}

else if (letter == m)
{
printf("Enter the two numbers you want to multiply");
scanf("%d", &num1);
scanf("%d", &num2);

answer = num1*num2;
printf("The answer is:%d", answer);
}

else if (letter == d)
{
printf("Enter the two numbers you want to divide");
scanf("%d", &num1);
scanf("%d", &num2);

answer = num1/num2;
printf("The answer is:%d", answer);
}
else 
{
printf("Please Try again");
}

return 0;
}

Could someone give me a hand please?

[laserlight]

You should use single quotes since they are character literals, e.g., 'a'.

[Elysia]

You need to indent your code, as well.

[darkphenom]

You should use single quotes since they are character literals, e.g., 'a'.

Thanks that worked!

[ungalnanban]

in your program you need to use the single quote.
because the variable type "letter" is char. your comparing the values using == . so it needs the ASCII value
if you use the switch statement that time you will use the case values in single quote for alphabets,
for integer values no need. the same things here happen.

so put single quote for 'a','s','m' and 'd'.