cs31 lecture 3

# 2 foo has value 36 float foo 12 242 foo has value

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Unformatted text preview: ample: foo = 12 + 24.2; x The type of the expression depends on the type of the The <lhs> <lhs> Example: int foo = 12 + 24.2; // foo has value 36 float foo = 12 + 24.2; // foo has value 36.2 x Be careful: floats are truncated to int, not rounded Example: int foo = 12 + 24.9; // foo has value 36 23 Integer division x Be careful: if division is used on integer data (variable or Be value), then integer division is used value), x Example: int foo = 3; foo = foo / 4; // foo has value 0 x Problem arises also for values Problem Example: float foo = 3 / 4; // foo has value 0 24 Integer division x To avoid the problem with values Add .f at the end of the number, to instruct the compiler to treat it Add as a float as • Example: float foo = 3.f / 4.f Add .0 at the end of the number to make it decimal • Example: float foo = 3.0 / 4.0 25 Common mistakes x Forgetting to declare a variable Forgetting The compiler tells you the error x Read the value of a variable before setting it Read The compiler *may* tell you the error IIn this case, the value of the variable at its first use is n undetermined undetermined x Use a type too small to hold the data The compiler usually doesnt tell anything x Make a mistake with integer division The compiler doesn’t tell you anything 26 A few examples 27 A first problem: compute the mpg of a car Algorithm MPG: IInput: nput: • m: number of miles since last refuel • g: number of gallons consumed since last refuel Output: • mpg: miles per gallon achieved 1.mpg := m / g 2.return mpg return 28 Now in C++ float MPG(float m, float g) { float mpg = m / g; float return mpg; return } int main() { float mpg = MPG(42, 10); float std::cout << “My mpg: “ << mpg << std::endl; std::cout } 29...
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