C 控制台程序使用用户输入（“+”/“-”）进行数学运算不起作用

Question

I made this program but it doesn't work.

You enter two numbers. Then you press + or -. If you press + it should add the numbers. If you press - it should subtract. But that part doesn't work.

#include <stdio.h>
#include <stdlib.h>

/* run this program using the console pauser or add your own getch, system("pause") or input loop */

int main(int argc, char *argv[]) {
char opt;       
int a,b,s;      
scanf("%d",&a);
scanf("%c\n",&opt);  
scanf("%d",&b); 
if(opt=='+') {           //this part doesn't work
s=a+b;
}
else if(opt=='-') {
s=a-b;
}
printf("%d",s);
 return 0;
}

What should I do?

Answer 1

scanf("%d",&a);
getchar();

Answer 2

Just remove \n from this line.. scanf("%c\n",&opt); So it will be... scanf("%c",&opt);

Answer 3

When you are using the conversion specifier %c then scanf reads all characters including white spaces.

Use the following call

scanf( " %c", &opt );
        ^^^ 

See the blank before the '%' symbol and the absent symbol '\n' .