C calculator if else - c

Question

I want to make a simple C calculator only with "IF" and "IF ELSE" conditions and it don't let me choose an operator ("+, -, * or /"), just appear my last if condition.
#include <stdio.h>
int main(){
printf("\tCalculadora\n\n");
int num1, num2, total;
char oper;
printf("Introduza o primeiro numero: \n");
scanf("%d", &num1);
printf("Introduza o segundo numero: \n");
scanf("%d", &num2);
printf("Escolha a operacao que quer realizar!\n\n");
scanf("%c", &oper);
if(oper == '+'){
printf("O resultado e: %d", num1+num2);
}
else if(oper == '-'){
printf("O resultado e: %d", num1-num2);
}
else if(oper == '*'){
printf("O resultado e: %d", num1*num2);
}
else{
printf("O resultado e: %d", num1/num2);
}
getchar();
getchar();
}

Answer 1

I avoid scanf() and its cousins. Here is a version of your calculator that uses fgets() for the input. It also uses double for the operands.
#include <stdio.h>
#include <stdlib.h>
#define ISIZE 100 // arbitrarily large
int main(){
double num1, num2;
int oper;
char inp[ISIZE+1] = "";
printf("\tCalculadora\n\n");
printf("Introduza o primeiro numero: "); // 1st operand
fgets (inp, ISIZE, stdin);
num1 = atof (inp);
printf("Introduza o segundo numero: "); // 2nd operand
fgets (inp, ISIZE, stdin);
num2 = atof (inp);
printf("Escolha a operacao que quer realizar! "); // operator
fgets (inp, ISIZE, stdin);
oper = inp[0];
printf ("O resultado e: %f %c %f = ", num1, oper, num2);
switch (oper) {
case '+': printf("%f\n", num1+num2); break;
case '-': printf("%f\n", num1-num2); break;
case '*': printf("%f\n", num1*num2); break;
case '/': if (num2!=0) printf("%f\n", num1/num2);
else printf ("Divisão por zero!\n");
break;
default: printf("Eu não sei o que operador\n");
}
return 0;
}

Answer 2

This
scanf("%c", &oper);
should change to
scanf(" %c", &oper);
so you let scanf() ignore the '\n' left by previous scanf()s.

Answer 3

I was also trying to apply my knowladage of C in a simple calculator and came across you question. In order to respect your if...else request I've come up with this solution. I hope this helps.
#include <stdio.h>
void sayHello( ) {
printf("Hello\n"); }
// to say hello to the user
int add( int num1, int num2) {
num1 = num1 + num2;
return num1;
}
int minus( int num1, int num2) {
num1 = num1 - num2;
return num1;
}
int times( int num1, int num2) {
num1 = num1 * num2;
return num1;
}
int divide( int num1, int num2) {
num1 = num1 / num2;
return num1;
}
// This is to declare the calculations
void flush_input(){
int ch;
while ((ch = getchar()) != '\n' && ch != EOF); }
// This is to flush the scanf values
// Kudos to Huw Collingbourne, Udemy Teacher
int main(int argc, char **argv) {
char c;
char f;
int n1;
int n2;
int total;
// n1 = ' ';
// n2 = ' ';
sayHello();
do {
c = ' ';
printf("Insert the type of Calculation you want to make:\n");
printf("A(d)dition, Subs(t)raction, Mu(l)tiplication, Di(v)ision: ");
c = getchar();
if(c == 'd') {
printf("\nInsert the first number:");
scanf("%d", &n1);
printf("Insert the second number:");
scanf("%d", &n2);
total = add( n1, n2 );
printf("%d plus %d equals to %d\n", n1, n2, total );
flush_input(); } else {
if( c == 't') {
printf("insert the base number:");
scanf("%d", &n1);
printf("Insert the subtracting number:");
scanf("%d", &n2);
total = minus( n1, n2 );
printf("The difference between %d and %d is %d\n", n1, n2, total );
flush_input(); } else {
if( c == 'l') {
printf("insert the first number:");
scanf("%d", &n1);
printf("Insert second number:");
scanf("%d", &n2);
total = times( n1, n2 );
printf("%d times %d equals %d\n", n1, n2, total );
flush_input(); } else {
if( c == 'v') {
printf("insert the first number:");
scanf("%d", &n1);
printf("Insert second number:");
scanf("%d", &n2);
total = divide( n1, n2 );
printf("%d divided by %d equals %d\n", n1, n2, total );
flush_input();
} else {
printf("I couln't understand the instruction\n Reseting program\n");
}
}
}
}
f = ' ';
printf("\nDo you wish to make another calculation?\n");
printf("Choose (y)es or (n)ot: ");
f = getchar();
// scanf("%c", &c);
getchar();
} while( f != 'n' );
printf("\nThat's all folks!\n");
return 0;
}

Answer 4

#include <stdio.h>
#include <stdlib.h>
//declaration of function
float cal (float a, float b, char o);
int main(int argc, char *argv[])
{
// declaration of variable
float num1,num2;
int inum1,inum2;
char o;
//initialization of variable
num1=0;
num2=0;
//input
printf("Enter 1st number\n");
scanf("%f",&num1);
//input
printf("operator\n");
scanf(" %c", &o);
//input
printf("Enter 2nd number\n");
scanf(" %f", &num2);
inum1=num1;
inum2=num2;
if(cal(num1,num2,o)==0)
{
printf("Math Error");
}
if(cal(num1,num2,o)==1)
{
printf("%d",inum1%inum2);
}
else
printf("%.3f\n",cal(num1,num2,o));
return 0;
}
//definening function
float cal (float a, float b, char o)
{
if (o=='+')
return a+b;
if (o=='-')
return a-b;
if (o=='*')
return a*b;
if (o=='%')
return 1;
if (o=='/')
if (b!=0)
return a/b;
if (b==0)
return 0;
}