left to right evaluation - c

Question

I am trying to carry out left to right evaluation in C. No order of precedence whatsoever. So 5+3*2 should be 16. I know how to do that with 2 numbers and an operator, however, I cannot figure out how to do the same thing for an expression like 2+4-5+2.
This is what I have for 2 numbers:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SIZE 20
int main(void)
{
char exp[SIZE];
int ans,c, i=0;
int length;
printf("Enter your expression: ");
fgets(exp, 20, stdin);
length = strlen(exp);
--length;
for(int j=0; j<length; j++)
{
while (exp[i]!='\n')
{
// putchar(exp[i]);
i++;
switch (exp[i])
{
case '+':
ans = (exp[i]-'0') + (exp[2]-'0');
printf("The answer is %d\n", ans);
break;
case '-':
ans = (exp[0]-'0') - (exp[2]-'0');
printf("The answer is %d\n", ans);
break;
case '*':
ans = (exp[0]-'0') * (exp[2]-'0');
printf("The answer is %d\n", ans);
break;
case '/':
ans = (exp[0]-'0') / (exp[2]-'0');
printf("The answer is %d\n", ans);
break;
default:
break;
}
}
}
exit(0);
}
Any help is appreciated.

Answer 1

Assuming alternating numbers and operators with single-character numbers (which seems to be what you assumed), a minimal implementation similar to your original implementation is:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SIZE 20
int main(void) {
char exp[SIZE];
int ans, length, i;
printf("Enter your expression: ");
fgets(exp, 20, stdin);
ans = exp[0] - '0';
length = strlen(exp) - 1;
for (i = 0; i < length && exp[i] != '\n'; i++) {
switch (exp[i]) {
case '+':
ans += exp[i+1] - '0';
break;
case '-':
ans -= exp[i+1] - '0';
break;
case '*':
ans *= exp[i+1] - '0';
break;
case '/':
ans /= exp[i+1] - '0';
break;
default:
break;
}
}
printf("The answer is %d\n", ans);
return 0;
}

Answer 2

As per your given example, assumed that each number will be single digit number.
Try this:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SIZE 20
int main(void)
{
char exp[SIZE];
int ans,c, i=0;
int length,j;
printf("Enter your expression: ");
fgets(exp, 20, stdin);
length = strlen(exp);
char ch;
ans = exp[i]-'0';
i++;
while (i <= length)
{
switch (exp[i])
{
case '+':
i++;
ans += (exp[i]-'0');
break;
case '-':
i++;
ans -=(exp[i]-'0');
break;
case '*':
i++;
ans *=(exp[i]-'0');
break;
case '/':
i++;
ans /= (exp[i]-'0');
break;
default:
break;
}
i++;
//printf("The answer is %d\n", ans);
}
printf("The answer is %d\n", ans);
exit(0);
}