Improve interest calculator to check for invalid inputs

src/interestCalculator.c

@@ -8,12 +8,21 @@ float timeInYears;
 
 printf("Please enter the principal amount:");
 scanf("%f",&principalAmount);
+if(principalAmount<=0){
+    return;
+}
 
 printf("\nPlease enter interest per year (percentage):");
 scanf("%f",&interestPerYear);
+if(interestPerYear<=0){
+    return;
+}
 
 printf("\nPlease enter interest time in years:");
 scanf("%f",&timeInYears);
+if(timeInYears<=0){
+    return;
+}
 
 float interestDecimal=interestPerYear/100;